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Automated tests

TLDR: do run v test-all locally, after making your changes, and before submitting PRs.

Tip: use v -cc tcc when compiling tests, because TCC is much faster, compared to most other C compilers like clang/gcc/msvc. Most test commands will use the V compiler and the V tools many times, potentially hundreds/thousands of times.

v test-all

Test and build everything. Usefull to verify locally, that the CI will most likely pass. Slowest, but most comprehensive.

It works, by running these in succession:


In the v repo there are many tests. The main types are:

_test.v tests - these are the normal V test files.

All test_ functions in these files, will be ran automatically by V's test framework.

NB 1: You can run test files one by one, with: v file_test.v - this will run the test_ functions in file_test.v, and will exit with a 0 exit code, if they all had 0 failing assertions.

v -stats file_test.v - this will run the test_ functions, and show a report about how much time it took to run each of them too.

NB 2: You can also run many test files at once (in parallel, depending on how many cores you have), with: v test folder - this will run all _test.v files in folder, recursively.

v -stats test folder - same, but will also produce timing reports about how fast each test_ function in each _test.v file ran.

v test vlib/v/tests:

This folder contains _test.v files, testing the different features of the V compiler. Each of them will be compiled, and all the features in them have to work (verified by assertions).

v vlib/v/tests/inout/compiler_test.v

This is a test runner, that checks whether the output of running a V program, matches an expected .out file. You can also check for code that does panic using this test runner - just paste the start of the panic() output in the corresponding .out file.

NB: these tests, expect to find a pair of .vv and .out files, in the folder: vlib/v/tests/inout

The test runner will run each .vv file, and will check that its output, matches the contents of the .out file with the same base name. This is particularly useful for checking that errors and panics are printed.

v vlib/v/gen/c/coutput_test.v

coutput_test.v is a test runner, that checks whether the generated C source code matches all expectations, specified in *.c.must_have files, in the folder vlib/v/gen/c/testdata/ .

Each .c.must_have file, has to have a corresponding .vv file.

Each .c.must_have file, consists of multiple lines. Each of these lines, should be present at least once in the output, when the .vv file is compiled with -o - .

v vlib/v/tests/run_project_folders_test.v

This test runner, checks whether whole project folders, can be compiled, and run.

NB: Each project in these folders, should finish with an exit code of 0, and it should output OK as its last stdout line.

v vlib/v/tests/known_errors/known_errors_test.v

This test runner, checks whether a known program, that was expected to compile, but did NOT, due to a buggy checker, parser or cgen, continues to fail. The negative programs are collected in the vlib/v/tests/known_errors/testdata/ folder. Each of them should FAIL to compile, due to a known/confirmed compiler bug/limitation.

The intended use of this, is for providing samples, that currently do NOT compile, but that a future compiler improvement WILL be able to compile, and to track, whether they were not fixed incidentally, due to an unrelated change/improvement. For example, code that triggers generating invalid C code can go here, and later when a bug is fixed, can be moved to a proper _test.v or .vv/.out pair, outside of the vlib/v/tests/known_errors/testdata/ folder.

Test building of actual V programs (examples, tools, V itself)

Formatting tests

In vlib/v/fmt/ there are:

This checks .out tests.

This verifies that all _keep.vv files in the vlib/v/fmt/tests/ folder, would be unchanged by v fmt -w, i.e. that the v source code formatter, generates a stable source output, that does not change, once it is already formatted once.

This checks that all V source files are formatted, and prints a summary. This is not required.

Check that most .v files, are invariant of v fmt runs.

This tests that all .v files in the current folder are already formatted. It is useful for adding to CI jobs, to guarantee, that future contributions will keep the existing source nice and clean.

Markdown/documentation checks:

Ensure that all .md files in the project are formatted properly, and that the V code block examples in them can be compiled/formatted too.

v test-self

Run vlib module tests, including the compiler tests.

v vlib/v/compiler_errors_test.v

This runs tests for:

NB: there are special folders, that compiler_errors_test.v will try to run/compile with specific options:

vlib/v/checker/tests/globals_run/ - -enable-globals run; results stored in .run.out files, matching the .vv ones.

NB 2: in case you need to modify many .out files, run twice in a row: VAUTOFIX=1 ./v vlib/v/compiler_errors_test.v This will fail the first time, but it will record the new output for each .vv file, and store it into the corresponding .out file. The second run should be now successfull, and so you can inspect the difference, and commit the new .out files with minimum manual effort.

NB 3: To run only some of the tests, use: VTEST_ONLY=mismatch ./v vlib/v/compiler_errors_test.v This will check only the .vv files, whose paths match the given filter.


This is a Github Actions configuration file, that runs various CI tests in the main V repository, for example: