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F# Compiler, Core Library and Visual F# Tools Tests

Quick start: Running Tests

To run tests, use variations such as the following, depending on which test suite and build configuration you want:

build.cmd test
build.cmd net40 test
build.cmd coreclr test
build.cmd vs test
build.cmd all test


It is recommended that you run tests from an elevated command prompt, as there are a couple of test cases which require administrative privileges.

Test Suites

The F# tests are split as follows:

  • FSharp Suite - Older suite with broad coverage of mainline compiler and runtime scenarios.

  • FSharpQA Suite - Broad and deep coverage of a variety of compiler, runtime, and syntax scenarios.

  • FSharp.Core.UnitTests - Validation of the core F# types and the public surface area of FSharp.Core.dll.

  • FSharp.Compiler.UnitTests - Validation of compiler internals.

  • VisualFSharp.UnitTests - Visual F# Tools IDE Unit Test Suite This suite exercises a wide range of behaviors in the F# Visual Studio project system and language service.

More Details

FSharp Suite

This is compiled using tests\fsharp\FSharp.Tests.FSharpSuite.fsproj to a unit test DLL which acts as a driver script. Each individual test is an NUnit test case, and so you can run it like any other NUnit test.

Tests are grouped in folders per area. Each test compiles and executes a test.fsx|fs file in its folder using some combination of compiler or FSI flags specified in the FSharpSuite test project.
If the compilation and execution encounter no errors, the test is considered to have passed.

There are also negative tests checking code expected to fail compilation.

See note about baseline under "Other Tips" bellow for tests checking expectations against "baseline" files.

FSharpQA Suite

The FSharpQA suite relies on Perl, StrawberryPerl64 package from nuget is used automatically by the test suite.

These tests use the framework to execute, however the easiest way to run them is via the build.cmd script, see usage examples.

Tests are grouped in folders per area. Each folder contains a number of source code files and a single env.lst file. The env.lst file defines a series of test cases, one per line.

Each test case runs an optional "pre command," compiles a given set of source files using given flags, optionally runs the resulting binary, then optionally runs a final "post command".

If all of these steps complete without issue, the test is considered to have passed.

Read more at tests/fsharpqa/

Test lists

For the FSharpQA suite, the list of test areas and their associated "tags" is stored at

tests\fsharpqa\source\test.lst   // FSharpQA suite

Tags are in the left column, paths to to corresponding test folders are in the right column. If no tags are specified, all tests will be run.

If you want to re-run a particular test area, the easiest way to do so is to set a temporary tag for that area in test.lst (e.g. "RERUN") and then pass that as an argument to build.cmd: build.cmd test-net40-fsharpqa include RERUN.

FSharp.Compiler.UnitTests, FSharp.Core.UnitTests, VisualFSharp.UnitTests

These are all NUnit tests. You can execute these tests individually via the Visual Studio NUnit3 runner extension or the command line via nunit3-console.exe.

Note that for compatibility reasons, the IDE unit tests should be run in a 32-bit process, using the --x86 flag to nunit3-console.exe

Logs and output

All test execution logs and result files will be dropped into the tests\TestResults folder, and have file names matching


Other Tips

Run as Administrator

Do this, or a handful of tests will fail.

Making the tests run faster

  • NGen-ing the F# bits (fsc, fsi, FSharp.Core, etc) will result in tests executing much faster. Make sure you run src\update.cmd with the -ngen flag before running tests.
  • The FSharp and FSharpQA suites will run test cases in parallel by default. You can comment out the relevant line (look for PARALLEL_ARG) to disable this.
  • By default, tests from the FSharpQA suite are run using a persistent, hosted version of the compiler. This speeds up test execution, as there is no need for the fsc.exe process to spin up repeatedly. To disable this, uncomment the relevant line (look for HOSTED_COMPILER).

Test outcome against baseline

FSharp Test Suite works with couples of .bsl (or .bslpp) files considered "expected" and called baseline, those are matched against the actual output which resides under .err or .vserr files of same name at the during test execution.

When working on changes generating conflicts with the baseline, you can use the helper script tests/fsharp/update.base.line.with.actuals.fsx to update all .bsl based on the matching .err file.

When doing so keep in mind to carefully review the diff before comitting updated baseline files.

.bslpp (baseline pre-process) files are specially designed to enable substitution of certain tokens to generate the .bsl file. You can look further about the pre-processing logic under tests/fsharp/TypeProviderTests.fs, this is used only for type provider tests for now.