In our current testing environment, we spend a significant amount of effort crafting end-to-end tests for error conditions that could easily be captured by unit tests (or we simply forgo some hard-to-setup and rare error conditions). Describe what we hope to accomplish by implementing unit tests, and explain some open questions and milestones. Discuss desired features for test frameworks/harnesses, and provide a preliminary comparison of several different frameworks. Coauthored-by: Calvin Wan <calvinwan@xxxxxxxxxx> Signed-off-by: Calvin Wan <calvinwan@xxxxxxxxxx> Signed-off-by: Josh Steadmon <steadmon@xxxxxxxxxx> --- Unit tests additionally provide stability to the codebase and can simplify debugging through isolation. Turning parts of Git into libraries[1] gives us the ability to run unit tests on the libraries and to write unit tests in C. Writing unit tests in pure C, rather than with our current shell/test-tool helper setup, simplifies test setup, simplifies passing data around (no shell-isms required), and reduces testing runtime by not spawning a separate process for every test invocation. This patch adds a project document describing our goals for adding unit tests, as well as a discussion of features needed from prospective test frameworks or harnesses. It also includes a WIP comparison of various proposed frameworks. Later iterations of this series will probably include a sample unit test and Makefile integration once we've settled on a framework. A rendered preview of this doc can be found at [2]. In addition to reviewing the document itself, reviewers can help this series progress by helping to fill in the framework comparison table. [1] https://lore.kernel.org/git/CAJoAoZ=Cig_kLocxKGax31sU7Xe4==BGzC__Bg2_pr7krNq6MA@xxxxxxxxxxxxxx/ [2] https://github.com/steadmon/git/blob/unit-tests-asciidoc/Documentation/technical/unit-tests.adoc TODOs remaining: - List rough priorities across comparison dimensions - Group dimensions into sensible categories - Discuss pre-existing harnesses for the current test suite - Discuss harness vs. framework features, particularly for parallelism - Figure out how to evaluate frameworks on additional OSes such as *BSD and NonStop - Add more discussion about desired features (particularly mocking) - Add dimension for test timing - Evaluate remaining missing comparison table entries Changes in v4: - Add link anchors for the framework comparison dimensions - Explain "Partial" results for each dimension - Use consistent dimension names in the section headers and comparison tables - Add "Project KLOC", "Adoption", and "Inline tests" dimensions - Fill in a few of the missing entries in the comparison table Changes in v3: - Expand the doc with discussion of desired features and a WIP comparison. - Drop all implementation patches until a framework is selected. - Link to v2: https://lore.kernel.org/r/20230517-unit-tests-v2-v2-0-21b5b60f4b32@xxxxxxxxxx Documentation/Makefile | 1 + Documentation/technical/unit-tests.txt | 196 +++++++++++++++++++++++++ 2 files changed, 197 insertions(+) create mode 100644 Documentation/technical/unit-tests.txt diff --git a/Documentation/Makefile b/Documentation/Makefile index b629176d7d..3f2383a12c 100644 --- a/Documentation/Makefile +++ b/Documentation/Makefile @@ -122,6 +122,7 @@ TECH_DOCS += technical/scalar TECH_DOCS += technical/send-pack-pipeline TECH_DOCS += technical/shallow TECH_DOCS += technical/trivial-merge +TECH_DOCS += technical/unit-tests SP_ARTICLES += $(TECH_DOCS) SP_ARTICLES += technical/api-index diff --git a/Documentation/technical/unit-tests.txt b/Documentation/technical/unit-tests.txt new file mode 100644 index 0000000000..e302a0e40f --- /dev/null +++ b/Documentation/technical/unit-tests.txt @@ -0,0 +1,196 @@ += Unit Testing + +In our current testing environment, we spend a significant amount of effort +crafting end-to-end tests for error conditions that could easily be captured by +unit tests (or we simply forgo some hard-to-setup and rare error conditions). +Unit tests additionally provide stability to the codebase and can simplify +debugging through isolation. Writing unit tests in pure C, rather than with our +current shell/test-tool helper setup, simplifies test setup, simplifies passing +data around (no shell-isms required), and reduces testing runtime by not +spawning a separate process for every test invocation. + +We believe that a large body of unit tests, living alongside the existing test +suite, will improve code quality for the Git project. + +== Definitions + +For the purposes of this document, we'll use *test framework* to refer to +projects that support writing test cases and running tests within the context +of a single executable. *Test harness* will refer to projects that manage +running multiple executables (each of which may contain multiple test cases) and +aggregating their results. + +In reality, these terms are not strictly defined, and many of the projects +discussed below contain features from both categories. + + +== Choosing a framework & harness + +=== Desired features + +[[tap-support]] +==== TAP support + +The https://testanything.org/[Test Anything Protocol] is a text-based interface +that allows tests to communicate with a test harness. It is already used by +Git's integration test suite. Supporting TAP output is a mandatory feature for +any prospective test framework. + +In the comparison table below, "True" means this is natively supported. +"Partial" means TAP output must be generated by post-processing the native +output. + +Frameworks that do not have at least Partial support will not be evaluated +further. + +[[diagnostic-output]] +==== Diagnostic output + +When a test case fails, the framework must generate enough diagnostic output to +help developers find the appropriate test case in source code in order to debug +the failure. + +[[parallel-execution]] +==== Parallel execution + +Ideally, we will build up a significant collection of unit test cases, most +likely split across multiple executables. It will be necessary to run these +tests in parallel to enable fast develop-test-debug cycles. + +In the comparison table below, "True" means that individual test cases within a +single test executable can be run in parallel. "Partial" means that test cases +are run serially within a single executable, but multiple test executables can +be run at once (with proper harness support). + +[[vendorable-or-ubiquitous]] +==== Vendorable or ubiquitous + +If possible, we want to avoid forcing Git developers to install new tools just +to run unit tests. So any prospective frameworks and harnesses must either be +vendorable (meaning, we can copy their source directly into Git's repository), +or so ubiquitous that it is reasonable to expect that most developers will have +the tools installed already. + +[[maintainable-extensible]] +==== Maintainable / extensible + +It is unlikely that any pre-existing project perfectly fits our needs, so any +project we select will need to be actively maintained and open to accepting +changes. Alternatively, assuming we are vendoring the source into our repo, it +must be simple enough that Git developers can feel comfortable making changes as +needed to our version. + +In the comparison table below, "True" means that the framework seems to have +active developers, that it is simple enough that Git developers can make changes +to it, and that the project seems open to accepting external contributions (or +that it is vendorable). "Partial" means that at least one of the above +conditions holds. + +[[major-platform-support]] +==== Major platform support + +At a bare minimum, unit-testing must work on Linux, MacOS, and Windows. + +In the comparison table below, "True" means that it works on all three major +platforms with no issues. "Partial" means that there may be annoyances on one or +more platforms, but it is still usable in principle. + +[[lazy-test-planning]] +==== Lazy test planning + +TAP supports the notion of _test plans_, which communicate which test cases are +expected to run, or which tests actually ran. This allows test harnesses to +detect if the TAP output has been truncated, or if some tests were skipped due +to errors or bugs. + +The test framework should handle creating plans at runtime, rather than +requiring test developers to manually create plans, which leads to both human- +and merge-errors. + +[[runtime-skippable-tests]] +==== Runtime-skippable tests + +Test authors may wish to skip certain test cases based on runtime circumstances, +so the framework should support this. + +[[scheduling-re-running]] +==== Scheduling / re-running + +The test harness scheduling should be configurable so that e.g. developers can +choose to run slow tests first, or to run only tests that failed in a previous +run. + +"True" means that the framework supports both features, "Partial" means it +supports only one (assuming proper harness support). + +[[mock-support]] +==== Mock support + +Unit test authors may wish to test code that interacts with objects that may be +inconvenient to handle in a test (e.g. interacting with a network service). +Mocking allows test authors to provide a fake implementation of these objects +for more convenient tests. + +[[signal-error-handling]] +==== Signal & error handling + +The test framework must fail gracefully when test cases are themselves buggy or +when they are interrupted by signals during runtime. + +[[coverage-reports]] +==== Coverage reports + +It may be convenient to generate coverage reports when running unit tests +(although it may be possible to accomplish this regardless of test framework / +harness support). + +[[project-kloc]] +==== Project KLOC + +WIP: The size of the project, in thousands of lines of code. All else being +equal, we probably prefer a project with fewer LOC. + +[[adoption]] +==== Adoption + +WIP: we prefer a more widely-used project. We'll need to figure out the best way +to measure this. + +[[inline-tests]] +==== Inline tests + +Can the tests live alongside production code in the same source files? This can +be a useful reminder for developers to add new tests, and keep existing ones +synced with new changes. + +=== Comparison + +[format="csv",options="header"] +|===== +Framework,"<<tap-support,TAP support>>","<<diagnostic-output,Diagnostic output>>","<<parallel-execution,Parallel execution>>","<<vendorable-or-ubiquitous,Vendorable or ubiquitous>>","<<maintainable-extensible,Maintainable / extensible>>","<<major-platform-support,Major platform support>>","<<lazy-test-planning,Lazy test planning>>","<<runtime--skippable-tests,Runtime- skippable tests>>","<<scheduling-re-running,Scheduling / re-running>>","<<mock-support,Mock support>>","<<signal-error-handling,Signal & error handling>>","<<coverage-reports,Coverage reports>>","<<project-kloc,Project KLOC>>","<<adoption,Adoption>>","<<inline-tests,Inline tests>>" +https://lore.kernel.org/git/c902a166-98ce-afba-93f2-ea6027557176@xxxxxxxxx/[Custom Git impl.],[lime-background]#True#,[lime-background]#True#,?,[lime-background]#True#,[lime-background]#True#,[lime-background]#True#,[lime-background]#True#,?,?,[red-background]#False#,?,?,?,?,? +https://cmocka.org/[cmocka],[lime-background]#True#,[lime-background]#True#,?,[red-background]#False#,[yellow-background]#Partial#,[yellow-background]#Partial#,?,?,?,[lime-background]#True#,?,?,?,?,? +https://libcheck.github.io/check/[Check],[lime-background]#True#,[lime-background]#True#,?,[red-background]#False#,[yellow-background]#Partial#,[lime-background]#True#,?,?,?,[red-background]#False#,?,?,?,?,? +https://github.com/rra/c-tap-harness/[C TAP],[lime-background]#True#,[red-background]#False#,?,[lime-background]#True#,[yellow-background]#Partial#,[yellow-background]#Partial#,?,?,?,[red-background]#False#,?,?,?,?,? +https://github.com/silentbicycle/greatest[Greatest],[yellow-background]#Partial#,?,?,[lime-background]#True#,[yellow-background]#Partial#,?,?,?,?,[red-background]#False#,?,?,?,?,? +https://github.com/Snaipe/Criterion[Criterion],[lime-background]#True#,?,?,[red-background]#False#,?,[lime-background]#True#,?,?,?,[red-background]#False#,?,?,?,?,? +https://github.com/zorgnax/libtap[libtap],[lime-background]#True#,?,?,?,?,?,?,?,?,?,?,?,?,?,? +https://www.kindahl.net/mytap/doc/index.html[MyTAP],[lime-background]#True#,?,?,?,?,?,?,?,?,?,?,?,?,?,? +https://nemequ.github.io/munit/[µnit],[red-background]#False#,-,-,-,-,-,-,-,-,-,-,-,-,-,- +https://github.com/google/cmockery[cmockery],[red-background]#False#,-,-,-,-,-,-,-,-,-,-,-,-,-,- +https://github.com/lpabon/cmockery2[cmockery2],[red-background]#False#,-,-,-,-,-,-,-,-,-,-,-,-,-,- +https://github.com/ThrowTheSwitch/Unity[Unity],[red-background]#False#,-,-,-,-,-,-,-,-,-,-,-,-,-,- +https://github.com/siu/minunit[minunit],[red-background]#False#,-,-,-,-,-,-,-,-,-,-,-,-,-,- +https://cunit.sourceforge.net/[CUnit],[red-background]#False#,-,-,-,-,-,-,-,-,-,-,-,-,-,- +|===== + +== Milestones + +* Settle on final framework +* Add useful tests of library-like code +* Integrate with Makefile +* Integrate with CI +* Integrate with + https://lore.kernel.org/git/20230502211454.1673000-1-calvinwan@xxxxxxxxxx/[stdlib + work] +* Run alongside regular `make test` target base-commit: a9e066fa63149291a55f383cfa113d8bdbdaa6b3 -- 2.41.0.255.g8b1d071c50-goog
