Clean up mocks on start

Functions/Describe.ps1

@@ -77,6 +77,7 @@ about_TestDrive
     if ($null -eq (& $SafeCommands['Get-Variable'] -Name Pester -ValueOnly -ErrorAction $script:IgnoreErrorPreference))
     {
         # User has executed a test script directly instead of calling Invoke-Pester
+        Remove-MockFunctionsAndAliases
         $Pester = New-PesterState -Path (& $SafeCommands['Resolve-Path'] .) -TestNameFilter $null -TagFilter @() -SessionState $PSCmdlet.SessionState
         $script:mockTable = @{}
     }

Functions/It.ps1

@@ -344,7 +344,7 @@ function Get-ParameterDictionary
         [scriptblock] $ScriptBlock
     )
 
-    $guid = [guid]::NewGuid().Guid
+    $guid = [Guid]::NewGuid().Guid
 
     try
     {

Functions/Mock.ps1

@@ -332,7 +332,7 @@ about_Mocking
             CallHistory             = @()
             DynamicParamScriptBlock = $dynamicParamScriptBlock
             Aliases                 = @()
-            BootstrapFunctionName   = [Guid]::NewGuid().ToString()
+            BootstrapFunctionName   = 'PesterMock_' + [Guid]::NewGuid().Guid
         }
 
         $mockTable["$ModuleName||$CommandName"] = $mock
@@ -1501,3 +1501,22 @@ function Test-IsClosure
         $null -ne ($matches[1] -as [guid])
     )
 }
+
+function Remove-MockFunctionsAndAliases {
+    # when a test is terminated (e.g. by stopping at a breakpoint and then stoping the execution of the script)
+    # the aliases and bootstrap functions for the currently mocked functions will remain in place
+    # Then on subsequent runs the bootstrap function will be picked up instead of the real command, 
+    # because there is still an alias associated with it, and the test will fail.
+    # So before putting Pester state in place we should make sure that all Pester mocks are gone
+    # by deleting every alias pointing to a function that starts with PesterMock_. Then we also delete the 
+    # bootstrap function.
+    foreach ($alias in (& $script:SafeCommands['Get-Alias'] -Definition "PesterMock_*"))
+    {
+        & $script:SafeCommands['Remove-Item'] "alias:/$($alias.Name)"
+    }
+
+    foreach ($bootstrapFunction in (& $script:SafeCommands['Get-Command'] -Name "PesterMock_*"))
+    {
+        & $script:SafeCommands['Remove-Item'] "function:/$($bootstrapFunction.Name)"
+    }
+}

Pester.psm1

@@ -35,6 +35,7 @@ $script:SafeCommands = @{
     'Export-ModuleMember' = Get-Command -Name Export-ModuleMember  -Module Microsoft.PowerShell.Core       @safeCommandLookupParameters
     'ForEach-Object'      = Get-Command -Name ForEach-Object       -Module Microsoft.PowerShell.Core       @safeCommandLookupParameters
     'Format-Table'        = Get-Command -Name Format-Table         -Module Microsoft.PowerShell.Utility    @safeCommandLookupParameters
+    'Get-Alias'           = Get-Command -Name Get-Alias            -Module Microsoft.PowerShell.Utility    @safeCommandLookupParameters
     'Get-ChildItem'       = Get-Command -Name Get-ChildItem        -Module Microsoft.PowerShell.Management @safeCommandLookupParameters
     'Get-Command'         = Get-Command -Name Get-Command          -Module Microsoft.PowerShell.Core       @safeCommandLookupParameters
     'Get-Content'         = Get-Command -Name Get-Content          -Module Microsoft.PowerShell.Management @safeCommandLookupParameters
@@ -818,6 +819,7 @@ New-PesterOption
         }
 
         $script:mockTable = @{}
+        Remove-MockFunctionsAndAliases
         $pester = New-PesterState -TestNameFilter $TestName -TagFilter ($Tag -split "\s") -ExcludeTagFilter ($ExcludeTag -split "\s") -SessionState $PSCmdlet.SessionState -Strict:$Strict -Show:$Show -PesterOption $PesterOption
 
         try