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Testing policy
===
Aims
---
* Maintainers should be able to make a release of GLib at any time, confident
that it will not contain regressions or obvious bugs with new functionality
* Speed up review of submitted changes by deferring some of the review effort
to automated testing
* Allow fast detection of bugs in new or changed code, particularly if they are
only present on platforms not regularly used by the maintainers
* Allow easy dynamic and static analysis of a significant proportion of the
GLib code
* Statistics on tests (such as pass/failure) should be easily and mechanically
collectable to allow analysis and highlight problems
* Code for tests and code for production should be easily separable so that
statistics on them can be grouped separately
* Performance measurement tools for GLib should be reusable over time to allow
comparable measurements to be collected and to discourage use of lower
quality and throwaway tests when prototyping improvements to GLib
Policy
---
* Tests must be written for all new code, and any existing code which is being
non-trivially modified (for example to fix a bug), to give confidence to the
author and reviewer of the changes that they are correct for all platforms
that GLib runs CI on.
* Tests live in the `{glib,gobject,gio}/tests` directories. This allows their
code to be counted separately when analysing statistics such as code
coverage.
- Performance tests live in `{glib,gobject,gio}/tests/performance`, as they
are executed and results interpreted differently due to giving a result on
a continuous scale rather than a pass/fail result.
* All tests must use the GTest framework, as it supports
[structured output](https://testanything.org/) which exposes test results to
the test runner for analysis.
- Use `g_test_bug()` and `g_test_summary()` in unit tests to link them to
contextual information in bug reports, and to provide a summary of what
each test checks and how it goes about doing those checks. Sometimes a
test’s behaviour can be quite complex, and needs to be explained so that
future developers can understand and build on such tests in future.
- Use the `g_assert_*()` functions inside unit tests, and do not use
`g_assert()`. The latter is compiled out when GLib is built with
`G_DISABLE_ASSERT`, and the former are not. The `g_assert_*()` functions
also give more helpful error messages on test failure.
* Performance tests must be able to be run unattended. In this mode they must
choose default argument values which check that the performance test
functions (i.e. without crashing) and doesn’t take too long to complete. This
is used to automatically verify that performance tests still work, as they
are typically used infrequently and are subject to bitrot.
* Code coverage reports must be used to demonstrate that unit tests reach all
newly submitted or significantly modified code, reaching all lines of code
and a significant majority of branches. If this is not enforced, code ends up
never being tested.
* Code should be structured to be testable, which is typically only possible by
writing tests at the same time as the code. Otherwise it is easy to design
APIs which cannot easily be unit tested, and once those APIs are stable it is
hard to retrofit tests to them.
* Parsers, network-facing code or code which handles untrusted user input must
have fuzz tests added, in the `fuzzing` directory. These are run by
[oss-fuzz](https://github.com/google/oss-fuzz/) and are very effective at
catching exploitable security issues. See the
[fuzzing README](../fuzzing/README.md) for more details.
* When fixing bugs in existing code, regression tests must be added when it is
straightforward to do so. If it’s difficult to do so (such as if the code
needs to be significantly restructured or APIs need to be changed), adding
the regression tests can be deferred to a follow-up issue so as not to slow
down bug fixing. In that case, the bug fix must be carefully manually tested
before being merged.
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