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Example Pester test for a PowerShell v5 Class
# Begin Testing
InModuleScope -ModuleName ToyBox -ScriptBlock {
Function Set-ObjectMockProperties ($object,[switch]$Exists)
# This function will load the object and set the global script variables with the values supplied.
# By doing this, we can later easily change how we interact with the object and make edits along
# the way in other Mocks or Tests.
New-VerboseMessage 'Establish Aggregate Mock variables and settings'
[string[]]$script:___CurrentState = $object.State
[int]$script:___CurrentFavorite = $object.Favorite
if ($Exists) {$script:DeadmanObjectCreatedTrigger = $true;}
else {$script:DeadmanObjectCreatedTrigger = $False;}
Function New-MockToyBox
# This function will act as a Mock for our existing New-ToyBox function. The benefit to this behavior is that
# we can easily stub out the expected responses for the call. We have included a Switch parameter call Empty
# to allow us the ability to return either an item with default values (in the event that we want to test the output)
# or an empty object to which we can assign any value.
$_mockToyBox = [ToyBox]::new() # The NEW() method is inherited by default for a class and does not need to be created.
if ($empty)
# Since the empty parameter was sent, we will need to return just be new object with no data.
return $_mockToyBox;
$_mockToyBox.Name = 'mytoy'
$_mockToyBox.State = 'Missing'
$_mockToyBox.Favorite = $false
return $_mockToyBox;
# This is a function of Mocks and makes life easier when we need to re-initialize Mocks between test suites. The benefit to
# to leveraging this function is seen when we have multiple suites that are not interdependent on each other. Each test should
# be treated as an independent state with no dependency on other tests. This will ensure that the code that we test meets all
# requirements and the correct behavior can be tested.
Function Set-MockInstances ()
Mock New-ToyBox{
New-VerboseMessage 'Mock New-ToyBox'
if ($script:DeadmanObjectCreatedTrigger) {
$ToyBox = New-MockToyBox
$ToyBox.Name = $___CurrentName
$ToyBox.State = $___CurrentState
$ToyBox.Favorite = $___CurrentFavorite
return $ToyBox
} else {
return (New-MockToyBox -Empty)
# When testing large sections of code, it is always a good idea to distinguish messages from your test and any that may come from
# your code. This function will handle the way that we print out the code moving forward.
Function New-VerboseMessage ($message)
$Classifier = '::PESTER:::::'
# NOTE: Interpolation of strings is a common trick that I use with messages. In this case, I have a message that I would like
# to inject the value of two variables. The '-f' identifies that these variables should be inserted into the string in and
# translated to their position in the array that follows. This allows me to easily make changes to the variables while maintaining
# and easy to read command. I typically use this technique in my large scripts, modules, and classes to streamline how I print the
# the output.
write-verbose -message ("{0}`t`t{1}" -f $Classifier, $Message)
# This an Array of properties that exist in our object and will be referenced in other tests to ensure
# all of the data is being returned from the Mocks. This should be a list of ALL the properties in
# the object scope.
$Test_Properties = @(
, 'State'
, 'Favorite'
# Establish both Passing and Failing Test Parameter Objects for using in the validation tests to streamline
# the behavior of the tests. Not setting a property will accept our defaults from the Mock
$negativeTestParameters = @{
Name = 'mytoy'
State = 'Missing'
Favorite = $false
$positiveTestParameters = @{
Name = 'my new toy'
State = 'Playing'
Favorite = $true
# ToyBox::get() Validation Tests
Describe -Name 'ToyBox Get() Tests' -Tags @('ToyBox','ToyBoxGet','Unit','Get') -Fixture {
Set-MockInstances # Initiate the instances of Mock Servers and Environments for the suite
Context 'When the Toy does not exist' {
BeforeAll {
# The BeforeAll will be triggered before each indiviual test to ensure that the data is
# loaded and ready. This gives us a clean slate opportunity between tests.
Set-ObjectMockProperties -object $negativeTestParameters
# Since our method contains an overload for the Name property when searching, we are goung to create
# a new instance of the ToyBox by calling our invoke function 'New-ToyBox' which ultimately leverages
# our Mock and then initiate a call to GET() based on the Name property for our $negativeTestParameters
# variable. Since this item does not exist, it will return a $NULL name and missing.
$result = (New-ToyBox @negativeTestParameters).get($negativeTestParameters.Name)
It 'Should return the name as $Null and State as Missing' {
$result.Name | Should be $Null
$result.State | Should Be 'Missing'
It 'Should call the mock function New-ToyBox' {
# Asserting a Mock is a great way to ensure that the behavior in this test matches the path that
# we expect our code to take. This is also a great way to capture inefficient code paths (Am I
# making too many calls to the same function, Did I call something that I shouldn't, etc)
# If the code should NOT call a mock (For example, if we have a function that would be called on a Save), then
# we can easily Asset that the Mock is called -Times 0. This trick will help to ensure that we don't have a mistake
# in the code pattern.
Assert-MockCalled New-ToyBox -Exactly -Times 1 -Scope Context
Context 'When the ToyExists' {
BeforeAll {
# We are testing the behvaior that the object should exist when called. We can leverage this call and include our trigger
# parameter -Exists to set the DeadmanObjectCreatedTrigger variable to $true. This allows us to stub the output with a valid
# object as if it was previously saved.
Set-ObjectMockProperties -object $positiveTestParameters -Exists
# We have multiple tests that need to call on the same data. In this case, we will return to the variable the object and use it
# across the multiple tests.
$result = (New-ToyBox @positiveTestParameters).get($positiveTestParameters.Name)
It 'Should return the desired state as Stored' {
$result.Name | Should Be 'my new toy'
$result.State | Should Be 'Playing'
$result.Favorite | Should Be $True
It 'Should return the same values as passed as parameters' {
# Previously we declared an array with all of our property names. We will now loop through this to ensure that we are returning
# the correct values based on our expectations. This because a very value test when we start changing values in later tests.
Foreach ($t in ($Test_Properties| Where-object {$_}))
New-VerboseMessage ("Testing ($t) : $($result.$($t)) | Should Be $( $positiveTestParameters.$($t) )")
$result.$($t) | Should Be $positiveTestParameters.$($t)
It 'Should call the mock function New-ToyBox' {
Assert-MockCalled New-ToyBox -Exactly -Times 1 -Scope Context
} #InModuleScope
} # try
# Done
} # finally
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