Invoke-Repro.ps1

rmo Pester -Force
ipmo Pester -MaximumVersion '4.0.8'
Invoke-Pester .\sut.ps1

rmo Pester -Force
ipmo Pester -MaximumVersion '3.6.0'
Invoke-Pester .\sut.ps1

<# Output:

Executing all tests in '.\sut.ps1'

Executing script .\sut.ps1

  Describing Pester version 4.0.8
    [+] Assert-MockCalled fails when -ParameterFilter returns nothing 87ms
    [+] Assert-MockCalled fails when -ParameterFilter explicitly returns $null 16ms
    [-] Assert-MockCalled passes when -ParameterFilter contains an assertion but returns nothing 50ms
      Expected: the expression not to throw an exception. Message was {Expected Invoke-SomethingInteresting to be called at least 1 times but was called 0 times}
          from C:\Users\brant.bobby\Documents\WindowsPowerShell\Modules\Pester\4.0.8\Functions\Mock.ps1:674 char:9
          +         throw ( New-ShouldErrorRecord -Message $failureMessage -Line  ...
          +         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      30:         } | Should Not Throw
      at Invoke-LegacyAssertion, C:\Users\brant.bobby\Documents\WindowsPowerShell\Modules\Pester\4.0.8\Functions\Assertions\Should.ps1: line 190
      at <ScriptBlock>, C:\Users\brant.bobby\Desktop\sut.ps1: line 26
    [+] Assert-MockCalled passes when -ParameterFilter performs an assertion and explicitly returns $true 21ms
Tests completed in 176ms
Tests Passed: 3, Failed: 1, Skipped: 0, Pending: 0, Inconclusive: 0


Describing Pester version 3.4.0
 [+] Assert-MockCalled fails when -ParameterFilter returns nothing 53ms
 [+] Assert-MockCalled fails when -ParameterFilter explicitly returns $null 13ms
 [+] Assert-MockCalled passes when -ParameterFilter contains an assertion but returns nothing 22ms
 [+] Assert-MockCalled passes when -ParameterFilter performs an assertion and explicitly returns $true 11ms
Tests completed in 101ms
Passed: 4 Failed: 0 Skipped: 0 Pending: 0 Inconclusive: 0
#>

sut.ps1

$pesterVersion = (Get-Module Pester).Version

# Just an arbitrary cmdlet which we will mock
function Invoke-SomethingInteresting
{
    [CmdletBinding()]param($Thing)
    $Thing
}

Describe "Pester version $pesterVersion" {
    Mock Invoke-SomethingInteresting {}

    Invoke-SomethingInteresting -Thing "foo"

    It "Assert-MockCalled fails when -ParameterFilter returns nothing" {
        { Assert-MockCalled Invoke-SomethingInteresting -ParameterFilter {} } | Should Throw
    }

    It "Assert-MockCalled fails when -ParameterFilter explicitly returns `$null" {
        {
            Assert-MockCalled Invoke-SomethingInteresting -ParameterFilter { return $null }
        } | Should Throw
    }

    It "Assert-MockCalled passes when -ParameterFilter contains an assertion but returns nothing" {
        {
            Assert-MockCalled Invoke-SomethingInteresting -ParameterFilter {
                $Thing | Should Be "foo"
            }
        } | Should Not Throw
    }
    It "Assert-MockCalled passes when -ParameterFilter performs an assertion and explicitly returns `$true" {
        {
            Assert-MockCalled Invoke-SomethingInteresting -ParameterFilter {
                $Thing | Should Be "foo"
                return $true
            }
        } | Should Not Throw
    }
}