testing-suite.md

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How to write tests?	section	The basics of writing a test suite with MUnit	3	testing-intro	testing-run

{% include markdown.html path="_markdown/install-munit.md" %}

Writing a test suite

A group of tests in a single class is called a test class or test suite.

Each test suite validates a particular component or feature of the software. Typically we define one test suite for each source file or class that we want to test.

{% tabs munit-unit-test-2 class=tabs-build-tool %} {% tab 'Scala CLI' %} In Scala CLI, the test file can live in the same folder as the actual code, but the name of the file must end with .test.scala. In the following, MyTests.test.scala is a test file.

example/
├── MyApp.scala
└── MyTests.test.scala

Other valid structures and conventions are described in the Scala CLI documentation. {% endtab %} {% tab 'sbt' %} In sbt, test sources go in the src/test/scala folder.

For instance, the following is the file structure of a project example:

example
└── src
    ├── main
    │   └── scala
    │       └── MyApp.scala
    └── test
        └── scala
            └── MyTests.scala

{% endtab %} {% tab 'Mill' %} In Mill, test sources go in the test/src folder.

For instance, the following is the file structure of a module example:

example
└── src
|   └── MyApp.scala
└── test
    └── src
        └── MyTests.scala

{% endtab %} {% endtabs %}

In the test source file, define a suite containing a single test:

{% tabs munit-unit-test-3 class=tabs-scala-version %} {% tab 'Scala 2' %}

package example

class MyTests extends munit.FunSuite {
  test("sum of two integers") {
    val obtained = 2 + 2
    val expected = 4
    assertEquals(obtained, expected)
  }
}

{% endtab %} {% tab 'Scala 3' %}

package example

class MyTests extends munit.FunSuite:
  test("sum of two integers") {
    val obtained = 2 + 2
    val expected = 4
    assertEquals(obtained, expected)
  }

{% endtab %} {% endtabs %}

A test suite is a Scala class that extends munit.FunSuite. It contains one or more tests, each defined by a call to the test method.

In the previous example, we have a single test "sum of integers" that checks that 2 + 2 equals 4. We use the assertion method assertEquals to check that two values are equal. The test passes if all the assertions are correct and fails otherwise.

Assertions

It is important to use assertions in each and every test to describe what to check. The main assertion methods in MUnit are:

• assertEquals to check that what you obtain is equal to what you expected
• assert to check a boolean condition

The following is an example of a test that use assert to check a boolean condition on a list.

{% tabs assertions-1 class=tabs-scala-version %} {% tab 'Scala 2' %}

test("all even numbers") {
  val input: List[Int] = List(1, 2, 3, 4)
  val obtainedResults: List[Int] = input.map(_ * 2)
  // check that obtained values are all even numbers
  assert(obtainedResults.forall(x => x % 2 == 0))
}

{% endtab %} {% tab 'Scala 3' %}

test("all even numbers") {
  val input: List[Int] = List(1, 2, 3, 4)
  val obtainedResults: List[Int] = input.map(_ * 2)
  // check that obtained values are all even numbers
  assert(obtainedResults.forall(x => x % 2 == 0))
}

{% endtab %} {% endtabs %}

MUnit contains more assertion methods that you can discover in its documentation: assertNotEquals, assertNoDiff, fail, and compileErrors.