haxe.unit, the unit testing package bundled in Haxe std library

Not sure if you knew, there has been a minimal basic unit testing package, haxe.unit, bundled in the Haxe std library, since Haxe 1.02! Although its functionality is minimal, but it is enough for most of the projects and being very target independent. I would definitely recommend it to any beginner of writing unit test.

The haxe.unit package consists of only 4 classes:

Most of the time we need to use only 2 of them: TestCase and TestRunner. We subclass TestCase and put the test functions as class methods, and then create a TestRunner object to run one or multiple TestCase instances. I usually create one class for each class I want to test and create one test method for each of the methods.

For example we want to test the StringTools class in the top-level package of the Haxe std library. Here we wrote the test function for 2 methods, endsWith and hex:

class TestStringTools extends haxe.unit.TestCase {
    public function testEndsWith():Void {
        this.assertTrue(StringTools.endsWith("abcd", "cd"));
        this.assertFalse(StringTools.endsWith("abcde", "cd"));

    public function testHex():Void {
        this.assertEquals("FFFFFF", StringTools.hex(0xFFFFFF, 6));
        this.assertEquals("000000", StringTools.hex(0, 6));

    static function main():Void {
        var runner = new haxe.unit.TestRunner();
        runner.add(new TestStringTools());
        var success = runner.run();

        #if sys
        Sys.exit(success ? 0 : 1);

As illustrated above, to check the return values of the function calls, there are 3 methods come from the TestCase class we can make use of:

They are self-explanatory. You may have noticed, they all accept an extra optional argument of type PosInfos, which is actually used for getting the method name, line number etc for printing the test result. We should simply ignore it and the compiler will automatically fill in the value.

Notice that the test methods have to be named with prefix “test”. We can create utility functions, without the “test” prefix, and they will be ignored by TestRunner.

To run the tests, we created a TestRunner in the main entry function. The main function can of course be put into another class, but since we’ve only one TestCase in this example, let’s just put it into our TestCase. When we call runner.run(), it will test all the TestCase objects that are added to the TestRunner, and immediately print the test result, which for our example, it would be:

Class: TestStringTools ..
OK 2 tests, 0 failed, 2 success

Lastly, based on the return value of runner.run(), which is “all tests success or not”, we exit the program properly as a best practice. It is used by many CI software, for example TravisCI, in order to get back the test result.

There exist more advanced unit testing frameworks, like munit and utest, but the structure and concept is somewhat similar. Anyway, writing unit test is easy and the benefit is huge: It will enables us to discover regression that may caused by refactoring, adding new features, changes in 3rd party library (or Haxe itself) as soon as possible. Let’s start doing it today if you haven’t!

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