Mocking with Pester

Pester
1

Hi,

I am trying to write a unit Pester test and not sure why I cannot get this to work. I am trying to verify that each code path works correctly. My function is below along with my Pester test. Please help! My function is calling an exposed Web Endpoint. I have tried different ways to mock out the responses but the common error I am getting is "You cannot call a method on a null-valued expression’ which is pointing to the $obj variable. I understand the error but I thought it would be bypassed since I am mocking the New-Object cmdlet.

Function

function Test-Endpoint {
    [CmdletBinding()]
    param(
        [Parameter(Mandatory=$true,
                    ValueFromPipeline=$true,
                    HelpMessage="Write anything to echo")]
        [string]$Message
    )
    Begin {
        $uris = 'x','y','z'
        Write-Verbose "URI's to test: $uris"
    }
    Process {
        Write-Verbose "Beginning Process block"
        foreach ($uri in $uris) {
            Try{
                $uri = "http://$uri/Something.svc/echo/$message"
                $request = Invoke-WebRequest   -Uri "$uri" `
                                    -Method 'Get' `
                                    -ContentType 'application/json' `
                                    -UseBasicParsing `
                                    -ErrorAction Stop
            } Catch {
                Write-Warning "$uri failed to return echo message"
                Write-Warning "$_.Exception.Message"
            }
            if($?) {
                Write-Verbose "Test $uri echo complete"
                $props = @{ 'URI' = $uri;
                            'StatusCode' = $request.StatusCode;
                            'Status' = $request.StatusDescription;
                            'Content' = $request.Content}
                $obj = New-object -TypeName PSObject -Property $props
                $obj.PSObject.TypeNames.Insert(0,'xyz.SystemInfo')
                Write-Output $obj
            }
        }
    }
    End {}
}

Pester Unit Test

Import-Module SomeModule

Describe "Test-Endpoint" {
    InModuleScope SomeModule {
        it 'attempts to return echo message if Invoke is successful' {
            mock -CommandName Invoke-WebRequest -MockWith {
                $request = @{'URI' = 'someURI';
                            'Content' = 'someContent';
                            'Status' = 'someStatus';
                            'StatusCode' = 'someStatusCode'
                            }
                return $request
            }
            mock -CommandName New-Object -MockWith {
                $obj = $result
                return $($obj.typeNames.Insert(0,'xyz.SystemInfo'))
            }
            Test-Endpoint -Message "SomeMessage"
            Assert-MockCalled -CommandName 'Invoke-WebRequest' -Times 1 -Scope It
            Assert-MockCalled -CommandName 'New-Object' -Times 1 -Scope It
        }
        it 'returns error message if invoke to endpoint fails' {
            mock -CommandName Invoke-WebRequest -MockWith {
                    return $Error
            }
            mock -CommandName 'New-Object' -MockWith { 
                return $null
            }
            Test-CorpSysBillingSummaryEcho -Message "someMessage"
            Assert-MockCalled Invoke-WebRequest -Times 1 -Scope It
            Assert-MockCalled New-Object -Times 0 -Scope It
        }   
    }    
}
2

You are mocking New-Object with the exact same code that’s actually running. I’d remove that mock and test that the function returns the expected object.

3

Hi,

3rd editing my response here. Sorry. What do you think about this? Is there a better way to do this? Any advice? I still want to create another Context block for when the codepath goes to Error. Not sure how to do that yet.

Import-Module SomeModule

Describe "Test-Endpoint" {
    InModuleScope SomeModule {
        Context 'Verifying success code path of echo method and expected fields are present & not null' {
            it 'attempts to invoke web api code path' {
                mock -CommandName Invoke-WebRequest -MockWith {
                    $request = @{'URI' = 'someURI';
                                'Content' = 'someContent';
                                'Status' = 'someStatus';
                                'StatusCode' = 'someStatusCode'
                                }
                    return $request
                }
                $global:result = Test-Endpoint -Message "SomeMessage"
                Assert-MockCalled -CommandName 'Invoke-WebRequest' -Times 1 -Scope It
            }
            it 'URI field exists and not null' {
                $result.URI.ToString() | Should Not Be $null
            }
            it 'Content field exists and not null' {
                $result.Content.ToString() | Should Not Be $null
            }
            it 'Status field exists and not null' {
                $result.Status.ToString() | Should Not Be $null
            }
            it 'StatusCode field exists and not null' {
                $result.StatusCode.ToString() | Should Not Be $null
            }
            it '4 NoteProperties exist' {
                ($result | Get-Member -MemberType NoteProperty).length | Should Be 4
            }
        }
    }
}