Continuous Delivery

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An book on the what, why, and how of measuring Continuous Delivery adoption within an organisation

The latest ebook from our founder Steve Smith is now available – “Measuring Continuous Delivery“.

Measuring Continuous Delivery” covers the what, why, and how of measuring Continuous Delivery adoption within an organisation. It is aimed at executives, managers, practitioners, and anyone else involved in Continuous Delivery adoption efforts.

From the introduction:

Continuous Delivery is a set of holistic principles and practices to reduce time to market and provide an organisation with a strategic competitive advantage, but adoption is invariably a challenging and time-consuming journey. Before adoption, the current time to market and desired time to market are often unknown, which makes alignment and collaboration between individuals, teams, and departments difficult. During adoption practices, techniques, and tools are often introduced without acceptance criteria, with makes it hard to assess and learn from the impact of changes.

What does a successful Continuous Delivery outcome look like, how do we move towards that outcome, and how do we measure our progress along the way?

Measuring Continuous Delivery” is being incrementally published on Leanpub in the weeks and months to come. Buy your copy today!

Buy “Measuring Continuous Delivery”

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An book on the what, why, and how of measuring Continuous Delivery adoption within an organisation

Announcing the latest ebook from our founder Steve Smith – “Measuring Continuous Delivery“.

Measuring Continuous Delivery” will cover the what, why, and how of measuring Continuous Delivery adoption within an organisation. It is aimed at executives, managers, practitioners, and anyone else involved in Continuous Delivery adoption efforts.

From the introduction:

Continuous Delivery is a set of holistic principles and practices to reduce time to market and provide an organisation with a strategic competitive advantage, but adoption is invariably a challenging and time-consuming journey. Before adoption, the current time to market and desired time to market are often unknown, which makes alignment and collaboration between individuals, teams, and departments difficult. During adoption practices, techniques, and tools are often introduced without acceptance criteria, with makes it hard to assess and learn from the impact of changes.

What does a successful Continuous Delivery outcome look like, how do we move towards that outcome, and how do we measure our progress along the way?

Measuring Continuous Delivery” will be incrementally published on Leanpub in the weeks and months to come. Register today and indicate your interest in this book!
Register your interest

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End-To-End Testing is used by many organisations, but relying on extensive end-to-end tests is fundamentally incompatible with Continuous Delivery. Why is End-To-End Testing so commonplace, and yet so ineffective?

In this article Steve Smith explains why End-To-End Testing is so undesirable and offers a lower-cost, higher-value Continuous Testing strategy focussed on antifragility. This article includes material from our popular Continuous Delivery For Managers and Continuous Delivery For Practitioners training courses.

Introduction

“Good testing involves balancing the need to mitigate risk against the risk of trying to gather too much information” Jerry Weinberg

Continuous Delivery is a set of holistic principles and practices to reduce time to market, and it is predicated upon rapid and reliable test feedback. Continuous Delivery mandates any change to code, configuration, data, or infrastructure must pass a series of automated and exploratory tests in a Deployment Pipeline to evaluate production readiness, so test execution times must be low and test results must be deterministic if an organisation is to achieve shorter lead times.

For example, consider a Company Accounts service in which year end payments are submitted to a downstream Payments service.

End-To-End Testing Considered Harmful - Company Accounts

The behaviour of the Company Accounts service could be checked at build time by the following types of automated test:

  • Unit tests check intent against implementation by verifying a discrete unit of code
  • Acceptance tests check implementation against requirements by verifying a functional slice of the system
  • End-to-end tests check implementation against requirements by verifying a functional slice of the system, including unowned dependent services

While unit tests and acceptance tests vary in terms of purpose and scope, acceptance tests and end-to-end tests vary solely in scope. Acceptance tests exclude unowned dependent services, so an acceptance test of a Company Accounts user journey would use a System Under Test comprised of the latest Company Accounts code and a Payments Stub.

End-To-End Testing Considered Harmful - A Company Accounts Acceptance Test

End-to-end tests include unowned dependent services, so an end-to-end test of a Company Accounts user journey would use a System Under Test comprised of the latest Company Accounts code and a running version of Payments.

End-To-End Testing Considered Harmful - A Company Accounts End-To-End Test

If a testing strategy is to be compatible with Continuous Delivery it must have an appropriate ratio of unit tests, acceptance tests, and end-to-end tests that balances the need for information discovery against the need for fast, deterministic feedback. If testing does not yield new information then defects will go undetected, but if testing takes too long delivery will be slow and opportunity costs will be incurred.

The folly of End-To-End Testing

“Any advantage you gain by talking to the real system is overwhelmed by the need to stamp out non-determinism” Martin Fowler

End-To-End Testing is a testing practice in which a large number of automated end-to-end tests and manual regression tests are used at build time with a small number of automated unit and acceptance tests. The End-To-End Testing test ratio can be visualised as a Test Ice Cream Cone.

End-To-End Testing Considered Harmful - The Test Ice Cream Cone

End-To-End Testing often seems attractive due to the perceived benefits of an end-to-end test:

  1. An end-to-end test maximises its System Under Test, suggesting a high degree of test coverage
  2. An end-to-end test uses the system itself as a test client, suggesting a low investment in test infrastructure

Given the above it is perhaps understandable why so many organisations adopt End-To-End Testing – as observed by Don Reinertsen, “this combination of low investment and high validity creates the illusion that system tests are more economical“. However, the End-To-End Testing value proposition is fatally flawed as both assumptions are incorrect:

  1. The idea that testing a whole system will simultaneously test its constituent parts is a Decomposition Fallacy. Checking implementation against requirements is not the same as checking intent against implementation, which means an end-to-end test will check the interactions between code pathways but not the behaviours within those pathways
  2. The idea that testing a whole system will be cheaper than testing its constituent parts is a Cheap Investment Fallacy. Test execution time and non-determinism are directly proportional to System Under Test scope, which means an end-to-end test will be slow and prone to non-determinism

Martin Fowler has warned before that “non-deterministic tests can completely destroy the value of an automated regression suite“, and Stephen Covey’s Circles of Control, Influence, and Concern highlights how the multiple actors in an end-to-end test make non-determinism difficult to identify and resolve. If different teams in the same Companies R Us organisation owned the Company Accounts and Payments services the Company Accounts team would control its own service in an end-to-end test, but would only be able to influence the second-party Payments service.

End-To-End Testing Considered Harmful - A Company Accounts End-To-End Test Single Organisation

The lead time to improve an end-to-end test depends on where the change is located in the System Under Test, so the Company Accounts team could analyse and implement a change in the Company Accounts service in a relatively short lead time. However, the lead time for a change to the Payments service would be constrained by the extent to which the Company Accounts team could persuade the Payments team to take action.

Alternatively, if a separate Payments R Us organisation owned the Payments service it would be a third-party service and merely a concern of the Company Accounts team.

End-To-End Testing Considered Harmful - A Company Accounts End-To-End Test Multiple Organisations

In this situation a change to the Payments service would take much longer as the Company Accounts team would have zero control or influence over Payments R Us. Furthermore, the Payments service could be arbitrarily updated with little or no warning, which would increase non-determinism in Company Accounts end-to-end tests and make it impossible to establish a predictable test baseline.

A reliance upon End-To-End Testing is often a symptom of long-term underinvestment producing a fragile system that is resistant to change, has long lead times, and optimised for Mean Time Between Failures instead of Mean Time To Repair. Customer experience and operational performance cannot be accurately predicted in a fragile system due to variations caused by external circumstances, and focussing on failure probability instead of failure cost creates an exposure to extremely low probability, extremely high cost events known as Black Swans such as Knights Capital losing $440 million in 45 minutes. For example, if the Payments data centre suffered a catastrophic outage then all customer payments made by the Company Accounts service would fail.

End-To-End Testing Considered Harmful - Company Accounts Payments Failure

An unavailable Payments service would leave customers of the Company Accounts service with their money locked up in in-flight payments, and a slow restoration of service would encourage dissatisfied customers to take their business elsewhere. If any in-flight payments were lost and it became public knowledge it could trigger an enormous loss of customer confidence.

End-To-End Testing is an uncomprehensive, high cost testing strategy. An end-to-end test will not check behaviours, will take time to execute, and will intermittently fail, so a test suite largely composed of end-to-end tests will result in poor test coverage, slow execution times, and non-deterministic results. Defects will go undetected, feedback will be slow and unreliable, maintenance costs will escalate, and as a result testers will be forced to rely on their own manual end-to-end regression tests. End-To-End Testing cannot produce short lead times, and it is utterly incompatible with Continuous Delivery.

The value of Continuous Testing

“Cease dependence on inspection to achieve quality. Eliminate the need for inspection on a mass basis by building quality into the product in the first place” Dr. W. Edwards Deming

Continuous Delivery advocates Continuous Testing – a testing strategy in which a large number of automated unit and acceptance tests are complemented by a small number of automated end-to-end tests and focussed exploratory testing. The Continuous Testing test ratio can be visualised as a Test Pyramid, which might be considered the antithesis of the Test Ice Cream Cone.

End-To-End Testing Considered Harmful - The Test Pyramid

Continuous Testing is aligned with Test-Driven Development and Acceptance Test Driven Development, and by advocating cross-functional testing as part of a shared commitment to quality it embodies the Continuous Delivery principle of Build Quality In. However, Continuous Testing can seem daunting due to the perceived drawbacks of unit tests and acceptance tests:

  1. A unit test or acceptance test minimises its System Under Test, suggesting a low degree of test coverage
  2. A unit test or acceptance test uses its own test client, suggesting a high investment in test infrastructure

While the End-To-End Testing value proposition is invalidated by incorrect assumptions of high test coverage and low maintenance costs, the inverse is true of Continuous Testing – its value proposition is validated by incorrect assumptions of low test coverage and high maintenance costs:

  1. A unit test will check intent against implementation and an acceptance test will check implementation against requirements, which means both the behaviour of a code pathway and its interactions with other pathways can be checked
  2. A unit test will restrict its System Under Test scope to a single pathway and an acceptance test will restrict itself to a single service, which means both can have the shortest possible execution time and deterministic results

A non-deterministic acceptance test can be resolved in a much shorter period of time than an end-to-end test as the System Under Test has a single owner. If Companies R Us owned the Company Accounts service and Payments R Us owned the Payments service a Company Accounts acceptance test would only use services controlled by the Company Accounts team.

End-To-End Testing Considered Harmful - Acceptance Test Multiple Organisations

If the Company Accounts team attempted to identify and resolve non-determinism in an acceptance test they would be able to make the necessary changes in a short period of time. There would also be no danger of unexpected changes to the Payments service impeding an acceptance test of the latest Company Accounts code, which would allow a predictable test baseline to be established.

End-to-end tests are a part of Continuous Testing, not least because the idea that testing the constituent parts of a system will simultaneously test the whole system is a Composition Fallacy. A small number of automated end-to-end tests should be used to validate core user journeys, but not at build time when unowned dependent services are unreliable and unrepresentative. The end-to-end tests should be used for release time smoke testing and runtime production monitoring, with synthetic transactions used to simulate user activity. This approach will increase confidence in production releases and should be combined with real-time monitoring of business and operational metrics to accelerate feedback loops and understand user behaviours.

In Continuous Delivery there is a recognition that optimising for Mean Time To Repair is more valuable than optimising for Mean Time Between Failures as it enables an organisation to minimise the impact of production defects, and it is more easily achievable. Defect cost can be controlled as Little’s Law guarantees smaller production releases will shorten lead times to defect resolution, and Continuous Testing provides the necessary infrastructure to shrink feedback loops for smaller releases. The combination of Continuous Testing and Continuous Delivery practices such as Blue Green Releases and Canary Releases empower an organisation to create a robust system capable of neutralising unanticipated events, and advanced practices such as Dark Launching and Chaos Engineering can lead to antifragile systems that seek to benefit from Black Swans. For example, if Chaos Engineering surfaced concerns about the Payments service the Company Accounts team might Dark Launch its Payments Stub into production and use it in the unlikely event of a Payments data centre outage.

End-To-End Testing Considered Harmful - Company Accounts Payments Stub Failure

While the Payments data centre was offline the Company Accounts service would gracefully degrade to collecting customer payments in the Payments Stub until the Payments service was operational again. Customers would be unaffected by the production incident, and if competitors to the Company Accounts service were also dependent on the same third-party Payments service that would constitute a strategic advantage in the marketplace. Redundant operational capabilities might seem wasteful, but Continuous Testing promotes operational excellence and as Nassim Nicholas Taleb has remarked “something unusual happens – usually“.

Continuous Testing can be a comprehensive and low cost testing strategy. According to Dave Farley and Jez Humble “building quality in means writing automated tests at multiple levels“, and a test suite largely comprised of unit and acceptance tests will contain meticulously tested scenarios with a high degree of test coverage, low execution times, and predictable test results. This means end-to-end tests can be reserved for smoke testing and production monitoring, and testers can be freed up from manual regression testing for higher value activities such as exploratory testing. This will result in fewer production defects, fast and reliable feedback, shorter lead times to market, and opportunities for revenue growth.

From end-to-end testing to continuous testing

“Push tests as low as they can go for the highest return in investment and quickest feedback” Janet Gregory and Lisa Crispin

Moving from End-To-End Testing to Continuous Testing is a long-term investment, and should be based on the notion that an end-to-end test can be pushed down the Test Pyramid by decoupling its concerns as follows:

  • Connectivity – can services connect to one another
  • Conversation – can services talk with one another
  • Conduct – can services behave with one another

Assume the Company Accounts service depends on a Pay endpoint on the Payments service, which accepts a company id and payment amount before returning a confirmation code and days until payment. The Company Accounts service sends the id and amount request fields and silently depends on the code response field.

End-To-End Testing Considered Harmful - Company Accounts Pay

The connection between the services could be unit tested using Test Doubles, which would allow the Company Accounts service to test its reaction to different Payments behaviours. Company Accounts unit tests would replace the Payments connector with a Mock or Stub connector to ensure scenarios such as an unexpected Pay timeout were appropriately handled.

The conversation between the services could be unit tested using Consumer Driven Contracts, which would enable the Company Accounts service to have its interactions continually verified by the Payments service. The Payments service would issue a Provider Contract describing its Pay API at build time, the Company Accounts service would return a Consumer Contract describing its usage, and the Payments service would create a Consumer Driven Contract to be checked during every build.

End-To-End Testing Considered Harmful - Company Accounts Consumer Driven Contract

With the Company Accounts service not using the days response field it would be excluded from the Consumer Contract and Consumer Driven Contract, so a build of the Payments service that removed days or added a new comments response field would be successful. If the code response field was removed the Consumer Driven Contract would fail, and the Payments team would have to collaborate with the Company Accounts team on a different approach.

The conduct of the services could be unit tested using API Examples, which would permit the Company Accounts service to check for behavioural changes in new releases of the Payments service. Each release of the Payments service would be accompanied by a sibling artifact containing example API requests and responses for the Pay endpoint, which would be plugged into Company Accounts unit tests to act as representative test data and warn of behavioural changes.

End-To-End Testing Considered Harmful - Company Accounts API Examples

If a new version of the Payments service changed the format of the code response field from alphanumeric to numeric it would cause the Company Accounts service to fail at build time, indicating a behavioural change within the Payments service and prompting a conversation between the teams.

Conclusion

“Not only won’t system testing catch all the bugs, but it will take longer and cost more – more than you save by skipping effective acceptance testing” – Jerry Weinberg

End-To-End Testing seems attractive to organisations due to its promise of high test coverage and low maintenance costs, but the extensive use of automated end-to-end tests and manual regression tests can only produce a fragile system with slow, unreliable test feedback that inflates lead times and is incompatible with Continuous Delivery. Continuous Testing requires an upfront and ongoing investment in test automation, but a comprehensive suite of automated unit tests and acceptance tests will ensure fast, deterministic test feedback that reduces production defects, shortens lead times, and encourages the Continuous Delivery of robust or antifragile systems.

Further Reading

  1. Continuous Delivery by Dave Farley and Jez Humble
  2. Principles Of Product Development Flow by Don Reinertsen
  3. 7 Habits of Highly Effective People by Stephen Covey
  4. Test Pyramid by Martin Fowler
  5. Test Ice Cream Cone by Alister Scott
  6. Integrated Tests Are A Scam by JB Rainsberger
  7. Agile Testing and More Agile Testing by Janet Gregory and Lisa Crispin
  8. Perfect Software and Other Illusions by Jerry Weinberg
  9. Release Testing Is Risk Management Theatre by Steve Smith
  10. The Art Of Agile Development by James Shore and Shane Warden
  11. Making End-To-End Tests Work by Adrian Sutton
  12. Just Say No To More End-To-End Tests by Mike Wacker
  13. Antifragile by Nassim Nicholas Taleb
  14. On Antifragility In Systems And Organisational Architecture by Jez Humble

Acknowledgements

Thanks to Amy Phillips, Beccy Stafford, Charles Kubicek, and Chris O’Dell for their early feedback on this article.

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Continuous Delivery often leads to the discovery of suboptimal practices within an organisation, and the Release Testing antipattern is a common example. What is Release Testing, and why is it an example of Risk Management Theatre?

In this article Steve Smith explains what Release Testing is, and why it is incompatible with Continuous Delivery. This topic is covered in our popular Continuous Delivery For Managers and Continuous Delivery For Practitioners training courses.

Pre-Agile Testing

“I was a principal test analyst. I worked in a separate testing team to the developers. I spent most of my time talking to them to understand their changes, and had to work long hours to do my testing” – Suzy

The traditional testing strategy of many IT organisations was predicated upon a misguided belief described by Elisabeth Hendrickson as “testers test, programmers code, and the separation of the two disciplines is important“. Segregated development and testing teams worked in sequential phases of the value stream, with each product increment handed over to the testers for a prolonged period of testing prior to sign-off.

Release Testing Is Risk Management Theatre - Pre Agile Testing

This strategy was certainly capable of uncovering defects, but it also had a detrimental impact on lead times and quality. The handover period between development and testing inserted delays into the value stream, creating large feedback loops that increased rework. Furthermore, the segregation of development and testing implicitly assigned authority for changes to developers and responsibility for quality to testers. This disassociated developers from defect consequences and testers from business requirements, invariably resulting in higher defect counts and lower quality over time.

Agile Testing

“I was a product tester. I worked in an agile team with developers and a business analyst. I contributed to acceptance tests and did exploratory testing. I don’t miss the old ways” – Dwayne

The publication of the Agile Manifesto in 2001 led to a range of lightweight development processes that introduced a radically different testing approach. Agile methods advocate cross-functional teams of co-located developers and testers, in which testing is considered a continuous activity and there is a shared commitment to product quality.

Release Testing Is Risk Management Theatre - Agile Testing

In an agile team developers and testers collaborate on practices such as Test Driven Development and Acceptance Test Driven Development in accordance with the Test Pyramid strategy, which recommends a large number of automated unit and acceptance tests in proportion to a small number of automated end-to-end and manual tests.

Release Testing Is Risk Management Theatre - Test Pyramid

The Test Pyramid favours automated unit and acceptance tests as they offer a greater value at a lower cost. Test execution time and determinism are directly proportional to System Under Test size, and as automated unit and acceptance tests have minimal scope they provide fast, deterministic feedback. Automated end-to-end tests and exploratory testing are also valuable, but the larger System Under Test means feedback is slower and less reliable.

This testing strategy is a vast improvement upon its predecessor. Uniting developers and testers in a product team eliminates handover delays and recombines authority with responsibility, resulting in a continual emphasis upon product quality and lower lead times.

Release Testing Is Risk Management Theatre - Agile Testing Test Pyramid

Release Testing

“I was an operational acceptance tester. I worked in a separate testing team to the developers and functional testers. I never had time to find defects or understand requirements, and always got the blame” – Jamie

The transition from siloed development and testing teams to cross-functional product teams is a textbook example of how organisational change enables Continuous Delivery – faster feedback and improved quality will unlock substantial cycle time gains and decrease opportunity costs. However, all too often Continuous Delivery is impeded by Release Testing – an additional phase of automated and/or manual end-to-end regression testing, performed on the critical path independent of the product team.

Release Testing Is Risk Management Theatre - Release Testing

Release Testing is often justified as a guarantee of product quality, but in reality it is a disproportionately costly practice with little potential for defect discovery. The segregation of release testers from the product team reinserts handover delays into the value stream and dilutes responsibility for quality, increasing feedback loops and rework. Furthermore, as release testers must rely upon end-to-end tests their testing invariably becomes a Test Ice Cream Cone of slow, brittle tests with long execution times and high maintenance costs.

Release Testing Is Risk Management Theatre - Test Ice Cream Cone

The reliance of Release Testing upon end-to-end testing on the critical path means a low degree of test coverage is inevitable. Release testers will always be working to a pre-arranged business deadline outside their control, and consequently test coverage will often be curtailed to such an extent the blameless testers will find it difficult to uncover any significant defects.

Release Testing Is Risk Management Theatre - Release Testing Test Ice Cream Cone

When viewed through a Continuous Delivery frame the high cost and low value of Release Testing become evident, and attempting to redress that imbalance is a zero-sum game. Decreasing the cost of Release Testing means fewer end-to-end tests, which will decrease execution time but also decrease test coverage. Increasing the value of Release Testing means more end-to-end tests, which will increase test coverage but also increase execution time. Release Testing can therefore be considered an example of what Jez Humble describes as Risk Management Theatre – an overly-costly practice with an artificial sense of value.

Release Testing is high cost, low value Risk Management Theatre

Build Quality In

Continuous Delivery is founded upon the Lean Manufacturing principle of Build Quality In, and the advice of Dr. W. Edwards Deming that “we cannot rely on mass inspection to improve quality” is especially pertinent to Release Testing. An organisation should build quality into its product rather than expect testers to inspect quality in at a later date, and that means eliminating Release Testing by moving release testers back into the product team.

Release Testing Is Risk Management Theatre - No Release Testing

Folding release testers into product development removes the handover delays and responsibility barriers imposed by Release Testing. End-to-end regression tests can be audited by all stakeholders, with valuable tests retained and the remainder discarded. More importantly, ex-release testers will be freed up to work on higher-value activities off the critical path, such as exploratory testing and business analysis.

Batch Size Reduction

Given the limited value of Release Testing it is prudent to consider other risk reduction strategies, and a viable alternative supported by Continuous Delivery is Batch Size Reduction – releasing smaller changesets more frequently into production. Splitting a large experiment into smaller independent experiments reduces variation in outcomes, so by decomposing large changesets into smaller unrelated changesets we can reduce the probability of failure associated with any one changeset.

For example, assume an organisation has a median cycle time of 12 weeks – perhaps due to Release Testing – and a pending release of 4 features. The probability of failure for this release has been estimated as 1 in 2 (50%), and there is a desire to reduce that level of risk.

Release Testing Is Risk Management Theatre - Probability One Release

As the 50% estimate is aggregated from 4 features it can be improved by reducing delivery costs – perhaps by eliminating Release Testing – and releasing features independently every 3 weeks. While this theoretically produces 4 homogeneous releases with a 1 in 8 (12.5%) failure probability, the heterogeneity of product development creates variable feature complexity – and smaller changesets enable more accurate estimation of comparative failure probabilities. In this example the 4 changesets allow a more detailed risk assessment that assigns features 2 and 3 a higher failure probability, which means more exploratory testing time can be allocated to those specific features to reduce overall failure probability.

Release Testing Is Risk Management Theatre - Probability Multiple Heterogenous Releases

When a production defect does occur, batch size reduction has the ability to significantly reduce defect cost. The cost of a defect is comprised of the sunk cost incurred between activation and discovery, and the opportunity cost incurred between discovery and resolution. Those costs are a function of cost per unit time and duration, where cost per unit time represents economic impact and duration represents time.

For example, assume the organisation unwisely retained its 12 week lead time and a production defect D1 has been found 3 weeks after release. An assessment of external market conditions calculates a static cost per unit time of £10,000 a week, which means a sunk cost of £30,000 has already been incurred and a £120,000 opportunity cost is looming.

Release Testing Is Risk Management Theatre - Opportunity Cost Long Lead Time

As cost per unit time is governed by external market conditions it is difficult to influence, but duration is controlled by Little’s Law which states that lead time is directly proportional to work in progress. This means the opportunity cost duration of a defect can be decreased by releasing the defect fix in a smaller changeset, which will result in a shorter lead time and a reduced defect cost. If a fix for D1 is released in its own changeset in 1 week, that would decrease the opportunity cost by 92% to £10,000 and produce a 73% overall reduction in defect cost to £40,000.

Release Testing Is Risk Management Theatre - Opportunity Cost Short Lead Time

Conclusion

Release Testing is the definitive example of Risk Management Theatre in the IT industry today and a significant barrier to Continuous Delivery. End-to-end regression testing on the critical path cannot provide any meaningful reduction in defect probability without incurring costs that harm product quality and inflate lead times. Continuous Delivery advocates a lower cost, higher value alternative in which the product team owns responsibility for product quality, with an emphasis upon exploratory testing and batch size reduction to decrease risk.

Tester names have been altered

Further Reading

  1. Leading Lean Software Development  by Mary and Tom Poppendieck
  2. Assign Responsibility And Authority by Shelley Doll
  3. Integrated Tests Are A Scam by JB Rainsberger
  4. Continuous Delivery by Dave Farley and Jez Humble
  5. Organisation Antipattern – Release Testing by Steve Smith
  6. The Essential Deming by W. Edwards Deming
  7. Explore It! by Elisabeth Hendrickson
  8. Principles Of Product Development Flow by Don Reinertsen

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The Version Control Strategies series

  1. Organisation Antipattern – Release Feature Branching
  2. Organisation Pattern – Trunk Based Development
  3. Organisation Antipattern – Integration Feature Branching
  4. Organisation Antipattern – Build Feature Branching

Build Feature Branching is oft-incompatible with Continuous Integration

Build Feature Branching is a version control strategy where developers commit their changes to individual remote branches of a source code repository prior to the shared trunk. Build Feature Branching is possible with centralised Version Control Systems (VCSs) such as Subversion and TFS, but it is normally associated with Distributed Version Control Systems (DVCSs) such as Git and Mercurial – particularly GitHub and GitHub Flow.

In Build Feature Branching Trunk is considered a flawless representation of all previously released work, and new features are developed on short-lived feature branches cut from Trunk. A developer will commit changes to their feature branch, and upon completion those changes are either directly merged into Trunk or reviewed and merged by another developer using a process such as a GitHub Pull Request. Automated tests are then executed on Trunk, testers manually verify the changes, and the new feature is released into production. When a production defect occurs it is fixed on a release branch cut from Trunk and merged back upon production release.

Consider an organisation that provides an online Company Accounts Service, with its codebase maintained by a team practising Build Feature Branching. Initially two features are requested – F1 Computations and F2 Write Offs – so F1 and F2 feature branches are cut from Trunk and developers commit their changes to F1 and F2.

Organisation Antipattern - Build Feature Branching - 1

Two more features – F3 Bank Details and F4 Accounting Periods – then begin development, with F3 and F4 feature branches cut from Trunk and developers committing to F3 and F4. F2 is completed and merged into Trunk by a non-F2 developer following a code review, and once testing is signed off on Trunk + F2 it is released into production. The F1 branch grows to encompass a Computations refactoring, which briefly breaks the F1 branch.

Organisation Antipattern - Build Feature Branching - 2

A production defect is found in F2, so a F2.1 fix for Write Offs is made on a release branch cut from Trunk + F2 and merged back when the fix is in production. F3 is deemed complete and merged into Trunk + F2 + F2.1 by a non-F3 developer, and after testing it is released into production. The F1 branch grows further as the Computations refactoring increases in scope, and the F4 branch is temporarily broken by an architectural change to the submissions system for Accounting Periods.

Organisation Antipattern - Build Feature Branching - 3

When F1 is completed the amount of modified code means a lengthy code review by a non-F1 developer and some rework are required before F1 can be merged into Trunk + F2 + F2.1 + F3, after which it is successfully tested and released into production. The architectural changes made in F4 also mean a time-consuming code review and merge into Trunk + F2 + F2.1 + F3 + F1 by a non-F4 developer, and after testing F4 goes into production. However, a production defect is then found in F4, and a F4.1 fix for Accounting Periods is made on a release branch and merged into Trunk + F2 + F2.1 + F3 + F1 + F4 once the defect is resolved.

Organisation Antipattern - Build Feature Branching - 4

In this example F1, F2, F3, and F4 all enjoy uninterrupted development on their own feature branches. The emphasis upon short-lived feature branches reduces merge complexity into Trunk, and the use of code reviews lowers the probability of Trunk build failures. However, the F1 and F4 feature branches grow unchecked until they both require a complex, risky merge into Trunk.

The Company Accounts Service team might have used Promiscuous Integration to reduce the complexity of merging each feature branch into Trunk, but that does not prevent the same code deviating on different branches. For example, integrating F2 and F3 into F1 and F4 would simplify merging F1 and F4 into Trunk later on, but it would not restrain F1 and F4 from generating Semantic Conflicts if they both modified the same code.

Organisation Antipattern - Build Feature Branching - 4 Promiscuous Merge

This example shows how Build Feature Branching typically inserts a costly integration phase into software delivery. Short-lived feature branches with Promiscuous Integration should ensure minimal integration costs, but the reality is feature branch duration is limited only by developer discipline – and even with the best of intentions that discipline is all too easily lost. A feature branch might be intended to last only for a day, but all too often it will grow to include bug fixes, usability tweaks, and/or refactorings until it has lasted longer than expected and requires a complex merge into Trunk. This is why Build Feature Branching is normally incompatible with Continuous Integration, which requires every team member to integrate and test their changes on Trunk on at least a daily basis. It is highly unlikely every member of a Build Feature Branching team will merge to Trunk daily as it is too easy to go astray, and while using a build server to continuously verify branch integrity is a good step it does not equate to shared feedback on the whole system.

Build Feature Branching advocates that the developer of a feature branch should have their changes reviewed and merged into Trunk by another developer, and this process is well-managed by tools such as GitHub Pull Requests. However, each code review represents a handover period full of opportunities for delay – the developer might wait for reviewer availability, the reviewer might wait for developer context, the developer might wait for reviewer feedback, and/or the reviewer might wait for developer rework. As Allan Kelly has remarked “code reviews lose their efficacy when they are not conducted promptly“, and when a code review is slow the feature branch grows stale and Trunk merge complexity increases. A better technique to adopt would be Pair Programming, which is a form of continuous code review with minimal rework.

Asking developers working on orthogonal tasks to share responsibility for integrating a feature into Trunk dilutes responsibility. When one developer has authority for a feature branch and another is responsible for its Trunk merge both individuals will naturally feel less responsible for the overall outcome, and less motivated to obtain rapid feedback on the feature. It is for this reason Build Feature Branching often leads to what Jim Shore refers to as Asynchronous Integration, where the developer of a feature branch starts work on the next feature immediately after asking for a review, as opposed to waiting for a successful review and Trunk build. In the short-term Asynchronous Integration leads to more costly build failures, as the original developer must interrupt their new feature and context switch back to the old feature to resolve a Trunk build failure. In the long-term it results in a slower Trunk build, as a slow build is more tolerable when it is monitored asynchronously. Developers will resist running a full build locally, developers will then checkin less often, and builds will gradually slowdown until the entire team grinds to a halt. A better solution is for developers to adopt Synchronous Integration in spite of Build Feature Branching, and by waiting on Trunk builds they will be compelled to optimise it using techniques such as acceptance test parallelisation.

Build Feature Branching works well for open-source projects where a small team of experienced developers must integrate changes from a disparate group of contributors, and the need to mitigate different timezones and different levels of expertise outweighs the need for Continuous Integration. However, for commercial software development Build Feature Branching fits the Wikipedia definition of an antipattern – “a common response to a recurring problem that is usually ineffective and risks being highly counterproductive“. A small, experienced team practising Build Feature Branching could theoretically accomplish Continuous Integration given a well-structured architecture and a predictable flow of features, but it would be unusual. For the vast majority of co-located teams working on commercial software Build Feature Branching is a costly practice that discourages collaboration, inhibits refactoring, and by implicitly sacrificing Continuous Integration acts as a significant impediment to Continuous Delivery. As Paul Hammant has said, “you should not make branches for features regardless of how long they are going to take“.

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