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Gherkin

This style is inspired by Cucumber's Gherkin syntax.

object SetFeature: Spek({
    Feature("Set") {
        val set by memoized { mutableSetOf<String>() }

        Scenario("adding items") {
            When("adding foo") {
                set.add("foo")
            }

            Then("it should have a size of 1") {
                assertEquals(1, set.size)
            }

            Then("it should contain foo") {
                assertTrue(set.contains("foo"))
            }
        }

        Scenario("empty") {
            Then("should have a size of 0") {
                assertEquals(0, set.size)
            }

            Then("should throw when first is invoked") {
                assertFailsWith(NoSuchElementException::class) {
                    set.first()
                }
            }
        }

        Scenario("getting the first item") {
            val item = "foo"
            Given("a non-empty set")  {
                set.add(item)
            }

            lateinit var result: String

            When("getting the first item") {
                result = set.first()
            }

            Then("it should return the first item") {
                assertEquals(item, result)
            }
        }
    }
})

Concepts

Feature

Purpose is to provide a high-level description of a software feature, and to group related scenarios.

Scenario

Describes a business rule, it consists of a list of steps. - Given: Describes the initial context or state of the scenario. - When: Describes an event or action. - Then: Describes the expected outcome or result. - And: Can be used as an alternative to additional Given, When, or Then steps.

Best practices

Validating a side-effect

Use Given to setup a context or some pre conditions. When describes the action, and Then Then describes the side effect (use multiple Thens if necessary).

Scenario("adding items") {
    When("adding foo") {
        set.add("foo")
    }

    Then("it should have a size of 1") {
        assertEquals(1, set.size)
    }

    Then("it should contain foo") {
        assertTrue(set.contains("foo"))
    }
}

Validating a return value

In cases were a return value needs checking, use lateinit variable to store the value.

Scenario("getting the first item") {
    val item = "foo"
    Given("a non-empty set")  {
        set.add(item)
    }

    lateinit var result: String

    When("getting the first item") {
        result = set.first()
    }

    Then("it should return the first item") {
        assertEquals(item, result)
    }
}