Matchers test for some property, indicated by the name of the matcher, beyond simple equality. For example, a matcher may check whether a string is empty or whether an integer is positive. In the getting started guide, we used the assertion shouldBe to check for equality. In fact, the assertion shouldBe also accepts a matcher that provides for more complicated assertions.

The idea behind the shouldBe naming convention is to lead to readable assertions, such as thisString shouldBe empty(). To further this goal, there is an equivalent of shouldBe, named should; with this, matchers such as thisString should startWith("foo") could be read as natural language.

Many matchers are provided by KotlinTest out of the box, and each one checks for some specific property or condition. In the rest of this section, we will cover some of the most fundamental matchers.