Test Framework

Flix comes with a built-in test framework. A test is a Flix function marked with the @Test annotation. A test function must take no arguments and return Unit.

The Assert module provides assertion functions for testing. Here are the most commonly used:

The assertEq and assertNeq functions require a labelled argument expected / unexpected.

Here is an example:

use Assert.{assertEq, assertTrue, assertFalse, assertOk, assertErr}

def add(x: Int32, y: Int32): Int32 = x + y

def isEven(x: Int32): Bool = Int32.modulo(x, 2) == 0

def safeDivide(x: Int32, y: Int32): Result[String, Int32] =
    if (y == 0) Err("Division by zero") else Ok(x / y)

@Test
def testAdd01(): Unit \ Assert =
    assertEq(expected = 5, add(2, 3))

@Test
def testIsEven01(): Unit \ Assert =
    assertTrue(isEven(4))

@Test
def testIsEven02(): Unit \ Assert =
    assertFalse(isEven(3))

@Test
def testSafeDivide01(): Unit \ Assert =
    assertOk(safeDivide(10, 2))

@Test
def testSafeDivide02(): Unit \ Assert =
    assertErr(safeDivide(10, 0))

Running the tests (e.g. with flix test) yields:

Running 5 tests...

   PASS  testAdd01 1,4ms
   PASS  testIsEven01 312,5us
   PASS  testIsEven02 229,8us
   PASS  testSafeDivide01 366,0us
   PASS  testSafeDivide02 299,7us

Passed: 5, Failed: 0. Skipped: 0. Elapsed: 3,8ms.

Assertions with Custom Messages

Most assertions have WithMsg variants for custom error messages.

use Assert.{assertEqWithMsg, assertTrueWithMsg, assertFalseWithMsg}

@Test
def testAdd01(): Unit \ Assert =
    assertEqWithMsg(expected = 5, add(2, 3), "addition should work")

@Test
def testIsEven01(): Unit \ Assert =
    assertTrueWithMsg(isEven(4), "4 should be even")

@Test
def testIsEven02(): Unit \ Assert =
    assertFalseWithMsg(isEven(3), "3 should be odd")

@Test Function Signatures

A function marked with @Test must have one of the following signatures:

@Test
def test01(): Unit = ...
def test02(): Unit \ Assert = ...
def test03(): Unit \ Assert + IO = ...

In addition, a @Test function may use any algebraic effect for which there is a @DefaultHandler.