Mocking with Pester

Pester provides a set of Mocking functions making it easy to fake dependencies and also to verify behavior. Using these mocking functions can allow you to "shim" a data layer or mock other complex functions that already have their own tests.

DESCRIPTION

With the set of Mocking functions that Pester exposes, one can:

• Mock the behavior of ANY powershell command.
• Verify that specific commands were (or were not) called.
• Verify the number of times a command was called with a set of specified parameters.

MOCKING FUNCTIONS

###Mock Mocks the behavior of an existing command with an alternate implementation.

###Assert-VerifiableMocks Checks if any Verifiable Mock has not been invoked. If so, this will throw an exception.

###Assert-MockCalled Checks if a Mocked command has been called a certain number of times and throws an exception if it has not.

EXAMPLE

function BuildIfChanged {
	$thisVersion=Get-Version
	$nextVersion=Get-NextVersion
	if($thisVersion -ne $nextVersion) {Build $nextVersion}
	return $nextVersion
}

$here = Split-Path -Parent $MyInvocation.MyCommand.Path
$sut = (Split-Path -Leaf $MyInvocation.MyCommand.Path).Replace(".Tests.", ".")
. "$here\$sut"

Describe "BuildIfChanged" {
	Context "Wnen there are Changes" {
		Mock Get-Version {return 1.1}
		Mock Get-NextVersion {return 1.2}
		Mock Build {} -Verifiable -ParameterFilter {$version -eq 1.2}

		$result = BuildIfChanged

        It "Builds the next version" {
            Assert-VerifiableMocks
        }
        It "returns the next version number" {
            $result.Should.Be(1.2)
        }
    }
	Context "Wnen there are no Changes" {
		Mock Get-Version -MockWith {return 1.1}
		Mock Get-NextVersion -MockWith {return 1.1}
		Mock Build -MockWith {}

		$result = BuildIfChanged

        It "Should not build the next version" {
            Assert-MockCalled Build -Times 0 -ParameterFilter{$version -eq 1.1}
        }
    }
}