Introduce ObjectConvertor for conversion to known API versions

Will allow clients to transform internal objects to a version
suitable for external output.

pkg/conversion/scheme_test.go

@@ -240,6 +240,45 @@ func TestMultipleNames(t *testing.T) {
 	}
 }
 
+func TestKnownTypes(t *testing.T) {
+	s := GetTestScheme()
+	if len(s.KnownTypes("v2")) != 0 {
+		t.Errorf("should have no known types for v2")
+	}
+
+	types := s.KnownTypes("v1")
+	for _, s := range []string{"TestType1", "TestType2", "TestType3", "ExternalInternalSame"} {
+		if _, ok := types[s]; !ok {
+			t.Errorf("missing type %q", s)
+		}
+	}
+}
+
+func TestConvertToVersion(t *testing.T) {
+	s := GetTestScheme()
+	tt := &TestType1{A: "I'm not a pointer object"}
+	other, err := s.ConvertToVersion(tt, "v1")
+	if err != nil {
+		t.Fatalf("Failure: %v", err)
+	}
+	converted, ok := other.(*ExternalTestType1)
+	if !ok {
+		t.Fatalf("Got wrong type")
+	}
+	if tt.A != converted.A {
+		t.Fatalf("Failed to convert object correctly: %#v", converted)
+	}
+}
+
+func TestConvertToVersionErr(t *testing.T) {
+	s := GetTestScheme()
+	tt := TestType1{A: "I'm not a pointer object"}
+	_, err := s.ConvertToVersion(tt, "v1")
+	if err == nil {
+		t.Fatalf("unexpected non-error")
+	}
+}
+
 func TestEncode_NonPtr(t *testing.T) {
 	s := GetTestScheme()
 	tt := TestType1{A: "I'm not a pointer object"}