Verify function experiment for use in Pester's Assert-MockCalled

verify.Tests.ps1

function Verify
{
    param
    (
        [Parameter(ValueFromPipeline,
                    Position = 1,
                    Mandatory)]
        $ExpressionResult
    )
    process
    {
        if ( $ExpressionResult -isnot [bool] )
        {
            throw "Verify failed: Expected $ExpressionResult to be boolean not $($ExpressionResult.GetType())."
        }
        if ( -not $ExpressionResult )
        {
            throw "Verify failed",
                  "$($PSCmdlet.MyInvocation.Line)" -join [System.Environment]::NewLine
        }
        $ExpressionResult
    }
}

Describe 'verify' {
    function f { param($a,$b) }
    Mock f -Verifiable
    Context 'success' {
        f -a 1 -b 2
        It 'several subexpressions' {
            Assert-MockCalled f 1 {
                ($a -eq 1 | Verify) -and
                ($b -eq 2 | Verify) -and
                ($b-1 -eq $a | Verify)
            }
        }
    }
    Context 'error message in Assert-MockCalled' {
        f -a 1 -b 2
        It 'single expression' {
            Assert-MockCalled f 1 {
                $a -eq 2 | Verify
            }
        }
        It 'multiple expressions, first line' {
            Assert-MockCalled f 1 {
                ($a -eq 2 | Verify) -and
                ($b -eq 2 | Verify) -and
                ($b-1 -eq $a | Verify)
            }
        }
        It 'multiple expressions, second line' {
            Assert-MockCalled f 1 {
                ($a -eq 1 | Verify) -and
                ($b -eq 1 | Verify) -and
                ($b-1 -eq $a | Verify)
            }
        }
        It 'multiple expressions, third line' {
            Assert-MockCalled f 1 {
                ($a -eq 1 | Verify) -and
                ($b -eq 2 | Verify) -and
                ($b -eq $a | Verify)
            }
        }
    }
}