SampleSnippet.ps1

#Function
#Get-Token and Get-PlainTextFromSecureString are private functions within the module

function Get-Projects
{
    [CmdletBinding()]
    [OutputType([Object[]])]
    param (
        [Parameter(Mandatory = $false)]
        [PSCredential]$Credential
    )

    Begin
    {
        $ErrorActionPreference = "Stop"
        if(-not ($PSBoundParameters.ContainsKey("Credential")))
        {
            $Credential = Get-Credential
        }
        $token = Get-Token $Credential
    }

    Process
    {
        $headers = @{
            'Authorization' = ("Bearer{0}" -f $token)
            'Content-Type' = 'application/json;v=1.0'
        }

        $results = Invoke-RestMethod -uri 'https://internalEndpoint.domain.corp/internalsoftware/projects' -Method GET -Headers $headers
        if(-not ($results.count -gt 0))
        {
            throw "There was an error retrieving a Projects.  Projects returned are empty."
        }
        $results
    }

    End
    {

    }
}


#Pester Test
#ModuleArtifact is the path to the IntermnModule file
Import-Module $ModuleArtifact -Verbose -Force

Describe "Get-Projects" {
    InModuleScope InternalModule {

        Mock Get-PlaintextFromSecureString {}

        Context "when not passing in a credential" {
            $password = ConvertTo-SecureString "Test1234!" -AsPlainText -Force
            $credential = New-Object System.Management.Automation.PSCredential ('TestUser', $password)
            Mock Get-Credential { $credential }
            Mock Invoke-RestMethod {}
            Mock Get-Token { "token" }

            It "Get-Credential is called prompting for a password" {
                GetProjects
                Assert-MockCalled Get-Credential -Exactly 1
                Assert-MockCalled Get-PlaintextFromSecureString -Exactly 1 -ParameterFilter { $SecurePassword -eq $credential.password }
            }
        }

        Context "when passing in a credential" {
            $password = ConvertTo-SecureString "Test1234!" -AsPlainText -Force
            $credential = New-Object System.Management.Automation.PSCredential ('TestUser', $password)
            $nonEmptyArray = @(1,2,3,4)
            Mock Invoke-RestMethod { $nonEmptyArray }
            Mock Get-Token { "token" }

            It "Get-Credential is not called prompting for a username and password" {
                GetProjects -Credential $credential
                Assert-MockCalled Get-Credential 0
            }
        }

        Context "when Invoke-RestMethod returns an empty empty array of projects" {
            $password = ConvertTo-SecureString "Test1234!" -AsPlainText -Force
            $credential = New-Object System.Management.Automation.PSCredential ('TestUser', $password)
            Mock Get-Token { "token" }

            It "GetProjects throws an exception" {
                $emptyArray = @()
                Mock Invoke-RestMethod { $emptyArray }
                { GetProjects -Credential $credential } | Should Throw "There was an error retrieving a Projects. Projects are empty."
                Assert-MockCalled Invoke-RestMethod -Exactly 1
            }
        }
    }
}

You mention you tried the Mock verbatim with what's working my side. Also you're on a more recent version of pester. So only two things I can think of trying.

1. Move Get-Credential out of Begin { .. } and into Process { .. }

I know it's not what you want, but worth a try. If it makes the difference then could consider some kind of a wrapper to avoid many calls to Get-Credential.

2. If it's not Pester that's the problem, then how about the version of Powershell. Maybe Get-Credential implementation changed at some stage.

The one other thing I can think of. I notice you have a Import-Module "path to module".
Probably unrelated to your issue, but I had problems with this is the past. Had to tidy up my module definitions and packaging slightly so that I no longer had to import via a path to the psm1 file. So for example, all my deployments look like this:

$env:PSModulePath = $env:PSModulePath + ";$($(Get-Location).Path)"
Import-Module Pivot.DockerAdmin

You probably know this stuff, but tripped me for a while. From my notes...

1. Make sure your code is packaged properly^ (note: dir name same as module and manifest, then you import from level-up that includes this manifest parent directory)
2. Include this folder in the PSModule path:
   1. Either by dropping it in one of the persistent paths.
   2. Or adding the path to it for the session**
3. Now just use "Import-Module Hue.Script" rather than "Import-Module .\Hue.Script.psm1"
   1. If you don't do this, the manifest isn't considered at all.
4. Make sure your manifest has the correct info - it's of critical importance now***
   1. E.g. include helper functions through NestedModules
   2. Include other files e.g. Const.psd1. Then can use within module like:
      1. $Const = Get-Content "$PSScriptRoot\Const.psd1" | Out-String | Invoke-Expression
      2. [or powershell 5+] >$Const = Import-PowerShellDataFile "$PSScriptRoot\Const.psd1"

^use this folder structure
root
--Hue.Script

----Hue.Script.psm1
----Hue.Script.psd1
----Nested.Module.psm1

You mention you tried the Mock verbatim with what's working my side. Also you're on a more recent version of pester. So only two things I can think of trying.

1. Move Get-Credential out of Begin { .. } and into Process { .. }

I know it's not what you want, but worth a try. If it makes the difference then could consider some kind of a wrapper to avoid many calls to Get-Credential.

1. If it's not Pester that's the problem, then how about the version of Powershell. Maybe Get-Credential implementation changed at some stage.

Tried moving into process block and same result. I'm using Powershell version 5.1 and may try experimenting with a different version. I'm even considering removing the get-credential call all together.

I'll keep experimenting and provide any updates here for future reference. I'll have to timebox this though for just today :/.

Thanks again!

The one other thing I can think of. I notice you have a Import-Module "path to module".
Probably unrelated to your issue, but I had problems with this is the past. Had to tidy up my module definitions and packaging slightly so that I no longer had to import via a path to the psm1 file. So for example, all my deployments look like this:

$env:PSModulePath = $env:PSModulePath + ";$($(Get-Location).Path)"
Import-Module Pivot.DockerAdmin

You probably know this stuff, but tripped me for a while. From my notes...

1. Make sure your code is packaged properly^ (note: dir name same as module and manifest, then you import from level-up that includes this manifest parent directory)

2. Include this folder in the PSModule path:
   
   1. Either by dropping it in one of the persistent paths.
   2. Or adding the path to it for the session**

3. Now just use "Import-Module Hue.Script" rather than "Import-Module .\Hue.Script.psm1"
   
   1. If you don't do this, the manifest isn't considered at all.

4. Make sure your manifest has the correct info - it's of critical importance now***
   
   1. E.g. include helper functions through NestedModules
   2. Include other files e.g. Const.psd1. Then can use within module like:
      
      1. $Const = Get-Content "$PSScriptRoot\Const.psd1" | Out-String | Invoke-Expression
      2. [or powershell 5+] >$Const = Import-PowerShellDataFile "$PSScriptRoot\Const.psd1"

^use this folder structure
root
--Hue.Script

----Hue.Script.psm1
----Hue.Script.psd1
----Nested.Module.psm1

Noted thanks!

@cathalmchale I ended up making the credential object a mandatory parameter which accomplishes the same goal. If I call my function without specifying a credential parameter, it prompts me using get-credential. I didn't need the logic around calling get-credential at all.