Describe

Creates a logical group of tests. All Mocks and TestDrive contents defined within a Describe block are scoped to that Describe; they will no longer be present when the Describe block exits. A Describe block may contain any number of Context and It blocks.

Parameters

Name

The name of the test group. This is often an expressive phrase describing the scenario being tested.

Fixture

The actual test script. If you are following the AAA pattern (Arrange-Act-Assert), this typically holds the arrange and act sections. The Asserts will also lie in this block but are typically nested each in its own It block. Assertions are typically performed by the Should command within the It blocks.

Tags

Optional parameter containing an array of strings. When calling Invoke-Pester, it is possible to specify a -Tag parameter which will filter Describe blocks containing the same Tag when the -PassThru parameter is enabled. In addition, if a Describe block has a tag, you can also use the -ExcludeTag when calling Invoke-Pester to exclude all Describe blocks with a certain tag.

Example

function Add-Numbers($a, $b) {
    return $a + $b
}

Describe "Add-Numbers" {
    It "adds positive numbers" {
        $sum = Add-Numbers 2 3
        $sum | Should Be 5
    }

    It "adds negative numbers" {
        $sum = Add-Numbers (-2) (-2)
        $sum | Should Be (-4)
    }

    It "adds one negative number to positive number" {
        $sum = Add-Numbers (-2) 2
        $sum | Should Be 0
    }

    It "concatenates strings if given strings" {
        $sum = Add-Numbers two three
        $sum | Should Be "twothree"
    }
}

Example with Tags

$tests = Invoke-Pester -ExcludeTag 'Disabled' -PassThru

Describe -Tag 'Disabled' "Add-Numbers" {
    It "adds positive numbers" {
        $sum = Add-Numbers 2 3
        $sum | Should Be 5
    }
}