Example of Testing DSC with Pester ( AWS Read S3 Object)

cReadS3Object.psm1

function Get-TargetResource
{
	[CmdletBinding()]
	[OutputType([System.Collections.Hashtable])]
	param
	(
		[parameter(Mandatory = $true)]
		[System.String]
		$Path,

        [parameter(Mandatory = $true)]
		[System.String]
		$BucketName,

		[parameter(Mandatory = $true)]
		[System.String]
		$Key,

        [parameter(Mandatory = $false)]
		[System.String]
		$ProfileName
	)

    # We are not checking in this whether the file is present (always return absent)

    Write-Verbose -Message "Creating hashtable."

	$returnValue = @{
		Path = $Path
        Key = $Key
        Bucket = $BucketName
		Ensure = "Absent"
	}

	$returnValue
}


function Set-TargetResource
{
	[CmdletBinding()]
	param
	(
		[parameter(Mandatory = $true)]
		[System.String]
		$Path,

        [parameter(Mandatory = $true)]
		[System.String]
		$BucketName,

		[parameter(Mandatory = $true)]
		[System.String]
		$Key,

        [parameter(Mandatory = $false)]
		[System.String]
		$ProfileName,

        [ValidateSet("Folder","File")]
        [System.String]
        $ItemType,

		[ValidateSet("Present","Absent")]
		[System.String]
		$Ensure
	)

    if($Ensure -eq "Present")
    {
        # Read the file from S3
        Write-Verbose -Message "Reading the File from S3"
        if($ItemType -eq "File")
        {
            if($ProfileName){

            Read-S3Object -BucketName $BucketName -Key $Key -ProfileName $ProfileName -File $Path
            }
            else{
            Read-S3Object -BucketName $BucketName -Key $Key -File $Path
            }
        }
        else{
        if($ProfileName){
                Read-S3Object -BucketName $BucketName -KeyPrefix $Key -Folder $Path -ProfileName $ProfileName
            }
            else{
                Read-S3Object -BucketName $BucketName -KeyPrefix $Key -Folder $Path
            }
        }
    }
    else
    {
        Write-Verbose -Message "Removing the file"
        #Remove the file
        Remove-Item -Path $Path -Force
    }
}


function Test-TargetResource
{
	[CmdletBinding()]
	[OutputType([System.Boolean])]
	param
	(
		[parameter(Mandatory = $true)]
		[System.String]
		$Path,

        [parameter(Mandatory = $true)]
		[System.String]
		$BucketName,

		[parameter(Mandatory = $true)]
		[System.String]
		$Key,

        [parameter(Mandatory = $false)]
		[System.String]
		$ProfileName,

		[ValidateSet("Present","Absent")]
		[System.String]
		$Ensure
	)


    $exists = Test-Path $Path

    if($Ensure = "Present")
    {
        $localhash = Get-FileHash $Path -Algorithm MD5

        $transformedHash = """$($localhash.Hash)"""

        $metaData = { Etag = ""}
        if($ProfileName){

                $metaData = Get-S3Object -ProfileName $ProfileName -Key $Key -BucketName $BucketName
        }
        else{
            Get-S3Object -Key $Key -BucketName $BucketName
        }
        return $transformedHash -eq $metaData.ETag
    }
    else{

        # Ensure file is absent
        return !$exists
    }
}


Export-ModuleMember -Function *-TargetResource

cReadS3Object.Tests.ps1

$here = Split-Path -Parent $MyInvocation.MyCommand.Path
$moduleName =  ($MyInvocation.MyCommand.Name -replace '^(.+?)\..*', '$1')

$sut = "..\DSCResources\$moduleName\$moduleName"
Import-Module "$here\$sut"

# Unit tests for IJYI_cAWSCredentials.schema.mof
 

Describe "S3 Bucket  Test-TargetResource" {
    
    $hash = Get-FileHash $MyInvocation.MyCommand.Name -Algorithm MD5

    Context "File is Present"{

    Mock Test-Path { return true }
    Mock Get-S3Object { return { ETag: $hash } }

    Context "when Ensure Present"{
    It "Test returns Present" {
        (Get-TargetResource -ProfileName $ProfileName).Ensure | Should Be "Absent"
    }
    
    
        It "Test returns True" {
            Test-TargetResource -ProfileName $ProfileName -Ensure Absent | Should Be $true
        }
    }
    
        It "Test returns False" {
            Test-TargetResource -ProfileName $ProfileName -Ensure Present | Should Be $false
        }
        It "Set Stores credentials" {
            ($ProfileName -in (Get-AWSCredentials -ListProfiles)) | Should Be $false
            Set-TargetResource -AccessKey $AccessKey -SecretKey $SecretKey -ProfileName $ProfileName -Ensure Present
            ($ProfileName -in (Get-AWSCredentials -ListProfiles)) | Should Be $true
        }
        AfterAll{
        Write-Verbose "Cleaning up Profile"
        Clear-AWSCredentials -ProfileName $ProfileName
        }
    }
    
    

}
Describe "S3 Bucket Get-Target Resource"{
    BeforeAll{
        Clear-AWSCredentials -ProfileName $ProfileName
        Set-AWSCredentials -AccessKey $AccessKey -SecretKey $SecretKey -StoreAs $ProfileName
    }
    It "Get returns Present" {
        (Get-TargetResource -ProfileName $ProfileName).Ensure | Should Be "Present"
    }
    Context "when Ensure Present"{
        It "Test returns True, if ensure Present" {
            Test-TargetResource -ProfileName $ProfileName -Ensure Present | Should Be $true
        }
    }
    Context "when Ensure Absent"{
        It "Test returns False, if ensure Absent" {
            Test-TargetResource -ProfileName $ProfileName -Ensure Absent | Should Be $false
        }
        It "Set Clears credentials, if ensure Absent " {
            ($ProfileName -in (Get-AWSCredentials -ListProfiles)) | Should Be $true
            Set-TargetResource -AccessKey $AccessKey -SecretKey $SecretKey -ProfileName $ProfileName -Ensure Absent
            ($ProfileName -in (Get-AWSCredentials -ListProfiles)) | Should Be $false
        }
        AfterAll{
        # Reset Credentials
            Clear-AWSCredentials -ProfileName $ProfileName
            Set-AWSCredentials -AccessKey $AccessKey -SecretKey $SecretKey -StoreAs $ProfileName
        }
    }
    AfterAll{
        Clear-AWSCredentials -ProfileName $ProfileName
    }
}

Test.ps1

Describe "S3 Bucket  Test-TargetResource" {

    Mock Test-Path { return true }
    Mock Get-S3Object { return { ETag: $hash } }

    Context "when Ensure Present"{
	    It "Test returns Absent" {
	        (Get-TargetResource -ProfileName $ProfileName).Ensure | Should Be "Absent"
	    }
    }
}