Make Out-Default -Transcript more robust in how it handles TranscribeOnly state (#3436)

test/powershell/Modules/Microsoft.PowerShell.Core/Out-Default.Tests.ps1

@@ -0,0 +1,40 @@
+Describe "Out-Default Tests" -tag CI {
+    BeforeAll {
+        # due to https://github.com/PowerShell/PowerShell/issues/3405, `Out-Default -Transcript` emits output to pipeline
+        # as running in Pester effectively wraps everything in parenthesis, workaround is to use another powershell
+        # to run the test script passed as a string
+        $powershell = "$PSHOME/powershell"
+    }
+
+    It "'Out-Default -Transcript' shows up in transcript, but not host" {
+        $script = @"
+            `$null = Start-Transcript -Path "$testdrive\transcript.txt";
+            'hello' | Microsoft.PowerShell.Core\Out-Default -Transcript;
+            'bye';
+            `$null = Stop-Transcript
+"@
+
+        & $powershell -c $script | Should BeExactly 'bye'
+        "TestDrive:\transcript.txt" | Should Contain 'hello'
+    }
+
+    It "Out-Default reverts transcription state when used more than once in a pipeline" {
+        & $powershell -c "Out-Default -Transcript | Out-Default -Transcript; 'Hello'" | Should BeExactly "Hello"
+    }
+
+    It "Out-Default reverts transcription state when exception occurs in pipeline" {
+        & $powershell -c "try { & { throw } | Out-Default -Transcript } catch {}; 'Hello'" | Should BeExactly "Hello"
+    }
+
+    It "Out-Default reverts transcription state even if Dispose() isn't called" {
+        $script = @"
+            `$sp = {Out-Default -Transcript}.GetSteppablePipeline();
+            `$sp.Begin(`$false);
+            `$sp = `$null;
+            [GC]::Collect();
+            [GC]::WaitForPendingFinalizers();
+            'hello'
+"@
+        & $powershell -c $script | Should BeExactly 'hello'
+    }
+}