Mocking with Pester

bschwede edited this page Dec 5, 2015 · 7 revisions

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.


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.



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


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


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


function Build ($version) {
    Write-Host "a build was run for version: $version"

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 "When 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" {
        It "returns the next version number" {
            $result | Should Be 1.2
    Context "When there are no Changes" {
        Mock Get-Version { return 1.1 }
        Mock Get-NextVersion { return 1.1 }
        Mock Build {}

        $result = BuildIfChanged

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

If you need to mock calls to commands which are made from inside a Script Module, additional code is required. For details, refer to Unit Testing within Modules