Fix serialization of PSCustomObject wrapped object

With the switch away from converting PSCustomObjects to dictionaries
we broke the way values that are wrapped in a PSCustomObject are serialized.

This is evident when values of hashtables are generated using Write-Output
which generates a PSCustomObject (Which is not evident in powershell, as
there is a lot of magic in powershell), but is clearly evident when we try
to use an object generated in PowerShell, in C#.

This change looks at the nested type of a PSCustomObject, and unwraps it
if it's not just another PSCustomObject.

Fixes: #157

Signed-off-by: Gabriel Adrian Samfira <gsamfira@cloudbasesolutions.com>

Tests/powershell-yaml.Tests.ps1

@@ -28,6 +28,21 @@ Import-Module $modulePath
 InModuleScope $moduleName {
     $compareStrictly = Get-EquivalencyOption -Comparator Equality
 
+    Describe "Test PSCustomObject wrapped values are serialized correctly" {
+        Context "Wrapped values" {
+            It "Should serialize correctly" {
+                $expectBigInt = [System.Numerics.BigInteger]::Parse("9999999999999999999999999999999999999999999999999")
+                $obj = [PSCustomObject]@{a = Write-Output 'string'; b = Write-Output 1; c = Write-Output @{nested = $true};d = [pscustomobject]$expectBigInt}
+                $asYaml = ConvertTo-Yaml $obj
+                $fromYaml = ConvertFrom-Yaml $asYaml
+
+                Assert-Equivalent -Options $compareStrictly -Expected "string" -Actual $fromYaml["a"]
+                Assert-Equivalent -Options $compareStrictly -Expected 1 -Actual $fromYaml["b"]
+                Assert-Equivalent -Options $compareStrictly -Expected $expectBigInt -Actual $fromYaml["d"]
+            }
+        }
+    }
+
     Describe "Test encode-decode symmetry." {
 
         Context "Simple-Items" {

src/PowerShellYamlSerializer.cs

@@ -81,7 +81,17 @@ public void WriteYaml(IEmitter emitter, object value, Type type, ObjectSerialize
                 emitter.Emit(new Scalar(AnchorName.Empty, "tag:yaml.org,2002:null", "", ScalarStyle.Plain, true, false));
             } else {
                 serializer(prop.Name, prop.Name.GetType());
-                serializer(prop.Value, prop.Value.GetType());
+                var objType = prop.Value.GetType();
+                var val = prop.Value;
+                if (prop.Value is PSObject nestedPsObj) {
+                    var nestedType = nestedPsObj.BaseObject.GetType();
+                    if (nestedType != typeof(System.Management.Automation.PSCustomObject)) {
+                        objType = nestedPsObj.BaseObject.GetType();
+                        val = nestedPsObj.BaseObject;
+                    }
+                }
+                serializer(val, objType);
+
             }
         }
         emitter.Emit(new MappingEnd());