unit-threaded 0.6.6

Advanced multi-threaded unit testing framework with minimal to no boilerplate

To use this package, run the following command in your project's root directory:

Manual usage
Put the following dependency into your project's dependences section:


Build Status

Multi-threaded unit test framework for D. Based on similar work for C++11.


"But doesn't D have built-in unittest blocks"? Yes, and they're massively useful. Even short scripts can benefit from them with 0 effort and setup. In fact, I use them to test this library. However, for larger projects it lacks some functionality:

  1. If all tests pass, great. If one fails, it's hard to know why.
  2. The only tool is assert, and you have to write your own assert messages (no assertEqual, assertNull, etc.)
  3. No possibility to run just one particular test
  4. Only runs in one thread.

So I wrote this library in and for a language with built-in support for unit tests. Its goals are:

  1. To run in parallel by default
  2. Support for built-in unittest blocks - no need to reinvent the wheel
  3. To be able to run specific tests or group of tests via the command-line
  4. No test registration. Tests are discovered with D's compile-time reflection
  5. Suppress tested code stdio and stderr output by default (important when running in multiple threads).
  6. Have a special mode that only works when using a single thread under which tested code output is turned back on, as well as special writelnUt debug messages.
  7. Ability to temporarily hide tests from being run by default whilst stil being able to run them

Quick start with dub

dub runs tests with dub test. Unfortunately, due to the nature of D's compile-time reflection, to use this library a test runner file listing all modules to reflect on must exist. Since this is a tedious task and easily automated, unit-threaded has a dub configuration called gen_ut_main to do just that. To use unit-threaded with a dub project, you can use a unittest configuration as exemplified in this dub.json:

    "name": "myproject",
    "targetType": "executable",
    "targetPath": "bin",
    "configurations": [
        { "name": "executable" },
            "name": "unittest",
            "preBuildCommands": ["dub run unit-threaded -c gen_ut_main -- -f bin/ut.d"],
            "mainSourceFile": "bin/ut.d",
            "excludedSourceFiles": ["src/main.d"],
            "dependencies": {
                "unit-threaded": "~>0.6.0"

excludedSourceFiles is there to not compile the file containing the main function to avoid linker errors. As an alternative to using excludedSourceFiles, the "real" main can be versioned out:

version(unittest) {}
else {
    void main() {

Your unittest blocks will now be run in threads and can be run individually. To name each unittest, simply attach a string UDA to it:

@("Test that 2 + 3 is 5")
unittest {
    assert(2 + 3 == 5);

You can also have multiple configurations for running unit tests, e.g. one that uses the standard D runtime unittest runner and one that uses unit-threaded:

"configurations": [
    {"name": "ut_default"},
      "name": "unittest",
      "preBuildCommands: ["dub run unit-threaded -c gen_ut_main -- -f bin/ut.d"],
      "mainSourceFile": "bin/ut.d",

In this example, dub test -c ut_default runs as usual if you don't use this library, and dub test runs with the unit-threaded test runner.

To use unit-threaded's assertions or UDA-based features, you must import the library:

version(unittest) { import unit_threaded; }
else              { enum ShouldFail; } // so production builds compile

int adder(int i, int j) { return i + j; }

@("Test adder") unittest {
    adder(2 + 3).shouldEqual(5);

@("Test adder fails", ShouldFail) unittest {
    adder(2 + 3).shouldEqual(7);

If using a custom dub configuration for unit-threaded as shown above, a version block can be used on Have_unit_threaded (this is added by dub to the build).

Advanced Usage, Attributes

@ShouldFail is used to decorate a test that is expected to fail, and can be passed a string to explain why. @ShouldFail should be preferred to @HiddenTest. If the relevant bug is fixed or not-yet-implemented functionality is done, the test will then fail, which makes them harder to sweep under the carpet and forget about.

Since code under test might not be thread-safe, the @Serial attribute can be used on a test. This causes all tests in the same module that have this attribute to be executed sequentially so they don't interleave with one another.

The @UnitTest and @DontTest attributes are explained below.

There is support for parameterized tests. This means running the test code multiple times, either with different values or different types. At the moment this feature cannot be used with the built-in unittest blocks.

For values and built-in unit tests, use the @Values UDA to supply test values and getValue with the appropriate type to retrive them:

@Values(2, 4, 6)
unittest {
    assert(getValue!int % 0 == 2);

You can also declare a test function that takes exactly one parameter of the type of the value to pass to it and add UDAs with the values desired, e.g.

@(2, 4, 6)
void testEven(int i) {
    (i % 0 == 2).shouldBeTrue;

In both cases the test code will be run 3 times, and the reporting will consider it to be 3 separate tests.

For types, use the @Types UDA on a template function with exactly one compile-time parameter:

@Types!(int, byte)
void testInit(T)() {

The @Name UDA can be used instead of a plain string in order to name a unittest block.

Command-line Parameters

There is support for debug prints in the tests with the -d switch. This is only supported in single-threaded mode (-s). Setting -d without -s will trigger a warning followed by the forceful use of -s. TestCases and test functions can print debug output with the function writelnUt available here.

Tests can be run in random order instead of in threads. To do so, use the -r option. A seed will be printed so that the same run can be repeated by using the --seed option. This implies running in a single thread.

Test Registration and Test Runner

There are two example programs in the example folder, one with passing unit tests and the other failing, to show what the output looks like in each case. Because of the way D packages work, they must be run from the top-level directory of the repository.

The built-in D unittest blocks are included automatically, as seen in the output of both example programs (example.tests.pass_tests.unittest and its homologue in example_fail). A name will be automatically generated for them. The user can specify a name by decorating them with a string UDA or the included @Name UDA.

The easiest way to run tests is by doing what the example code does: calling runTests() in runner.d with the modules containing the tests as compile-time arguments. This can be done as symbols or strings, and the two approaches are shown in the examples.

There is no need to register tests. The registration is implicit and happens with:

  • D's unittest` blocks
  • Functions with a camelCase name beginning with test (e.g. testFoo())
  • Classes that derive from TestCase and override test()

The modules to be reflected on must be specified when calling runTests, but that's usually done as shown in the dub configuration above. Private functions are skipped. TestCase also has support for setup() and shutdown(), child classes need only override the appropriate functions(s).

Don't like the algorithm for registering tests? Not a problem. The attributes @UnitTest and @DontTest can be used to opt-in or opt-out. These are used in the examples. Tests can also be hidden with the @HiddenTest attribute. This means that particular test doesn't get run by default but can still be run by passing its name as a command-line argument. HiddenTest takes a compile-time string to list the reason why the test is hidden. This would usually be a bug id but can be anything the user wants.

Since D packages are just directories and there the compiler can't read the filesystem at compile-time, there is no way to automatically add all tests in a package. To mitigate this and avoid having to manually write the name of all the modules containing tests, a dub configuration called gen_ut_main runs unit-threaded as a command-line utility to write the file for you.

  • dunit: xUnit Testing Framework for D
  • DMocks-revived: a mock-object framework that allows to mock interfaces or classes
  • deject: automatic dependency injection
  • specd: a unit testing framework inspired by specs2 and ScalaTest
  • DUnit: a toolkit of test assertions and a template mixin to enable mocking
  • Atila Neves
2.1.9 2024-Jan-23
2.1.8 2023-Nov-02
2.1.7 2023-Jul-31
2.1.6 2023-Apr-25
2.1.5 2023-Mar-17
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