add common helpers

helpers/pester-extensions.psm1

@@ -0,0 +1,33 @@
+<#
+.SYNOPSIS
+Pester extension that allows to run command and validate exit code
+.EXAMPLE
+"python file.py" | Should -ReturnZeroExitCode
+#>
+function ShouldReturnZeroExitCode {
+    Param(
+        [Parameter (Mandatory = $true)] [ValidateNotNullOrEmpty()]
+        [String]$ActualValue,
+        [switch]$Negate
+    )
+
+    Write-Host "Run command '${ActualValue}'"
+    Invoke-Expression -Command $ActualValue | ForEach-Object { Write-Host $_ }
+    $actualExitCode = $LASTEXITCODE
+
+    [bool]$succeeded = $actualExitCode -eq 0
+    if ($Negate) { $succeeded = -not $succeeded }
+
+    if (-not $succeeded)
+    {
+        $failureMessage = "Command '${ActualValue}' has finished with exit code ${actualExitCode}"
+    }
+
+    return New-Object PSObject -Property @{
+        Succeeded      = $succeeded
+        FailureMessage = $failureMessage
+    }
+}
+
+Add-AssertionOperator -Name ReturnZeroExitCode `
+                    -Test  $function:ShouldReturnZeroExitCode