test(include): add Invoke-PrivateContext helper to call private module functions

Test/include/callPrivateContext.ps1

@@ -0,0 +1,28 @@
+# CALL PRIVATE FUNCTIONS
+#
+# This file enables tests to invoke private (non-exported) functions
+# defined inside the main module by evaluating a provided scriptblock
+# in the module context.
+#
+# It relies on variables initialized by module.helper.ps1.
+# REQUIRED:
+#   $MODULE_PATH  - Full path to the module .psm1 file (or a file inside its folder)
+#
+# THIS INCLUDE REQUIRES module.helper.ps1
+if(-not $MODULE_PATH){ throw "Missing MODULE_PATH variable initialization. Check for module.helper.ps1 file." }
+
+function Invoke-PrivateContext {
+    param (
+        [Parameter(Mandatory, Position = 0)]
+        [scriptblock]$ScriptBlock
+    )
+
+    $modulePath = $MODULE_PATH | Split-Path -Parent
+    $module = Import-Module -Name $modulePath -PassThru
+
+    if ($null -eq $module) {
+        throw "Failed to import the main module."
+    }
+
+    & $module $ScriptBlock 
+} Export-ModuleMember -Function Invoke-PrivateContext

Test/public/callPrivateFunction.test.ps1

@@ -0,0 +1,27 @@
+function Test_InvokePrivateFunction{
+
+    # First check that private function call fails
+    $errorStr = @"
+The term 'Get-PrivateString' is not recognized as a name of a cmdlet, function, script file, or executable program.
+Check the spelling of the name, or if a path was included, verify that the path is correct and try again.
+"@
+
+    $hasthrown = $false
+    try{
+        Get-PrivateString -Param1 "TestParam"
+    } catch {
+        $hasthrown = $true
+        Assert-AreEqual -Expected $errorStr -Presented $_.Exception.Message
+    }
+    Assert-IsTrue -Condition $hasthrown
+
+
+    # Call private function through Invoke-PrivateContext
+    Invoke-PrivateContext {
+
+        $result = Get-PrivateString -Param1 "TestParam"
+
+        Assert-AreEqual -Expected "Private string [TestParam]" -Presented $result
+    }
+
+}