diff --git a/msg_test.go b/msg_test.go
index 3ce2b63..62c74ae 100644
--- a/msg_test.go
+++ b/msg_test.go
@@ -6037,6 +6037,46 @@ func TestMsg_HasSendError(t *testing.T) {
 	})
 }
 
+func TestMsg_WriteToTempFile(t *testing.T) {
+	if os.Getenv("PERFORM_UNIX_OPEN_WRITE_TESTS") != "true" {
+		t.Skipf("PERFORM_UNIX_OPEN_WRITE_TESTS variable is not set. Skipping unix open/write tests")
+	}
+
+	t.Run("WriteToTempFile succeeds", func(t *testing.T) {
+		message := testMessage(t)
+		tempFile, err := message.WriteToTempFile()
+		if err != nil {
+			t.Fatalf("failed to write message to temp file: %s", err)
+		}
+		parsed, err := EMLToMsgFromFile(tempFile)
+		if err != nil {
+			t.Fatalf("failed to parse message in buffer: %s", err)
+		}
+		checkAddrHeader(t, parsed, HeaderFrom, "WriteTo", 0, 1, TestSenderValid, "")
+		checkAddrHeader(t, parsed, HeaderTo, "WriteTo", 0, 1, TestRcptValid, "")
+		checkGenHeader(t, parsed, HeaderSubject, "WriteTo", 0, 1, "Testmail")
+		parts := parsed.GetParts()
+		if len(parts) != 1 {
+			t.Fatalf("expected 1 parts, got: %d", len(parts))
+		}
+		if parts[0].contentType != TypeTextPlain {
+			t.Errorf("expected contentType to be %s, got: %s", TypeTextPlain, parts[0].contentType)
+		}
+		if parts[0].encoding != EncodingQP {
+			t.Errorf("expected encoding to be %s, got: %s", EncodingQP, parts[0].encoding)
+		}
+		messageBuf := bytes.NewBuffer(nil)
+		_, err = parts[0].writeFunc(messageBuf)
+		if err != nil {
+			t.Errorf("writer func failed: %s", err)
+		}
+		got := strings.TrimSpace(messageBuf.String())
+		if !strings.HasSuffix(got, "Testmail") {
+			t.Errorf("expected message buffer to contain Testmail, got: %s", got)
+		}
+	})
+}
+
 /*
 // TestMsg_hasAlt tests the hasAlt() method of the Msg
 
diff --git a/msg_unix_test.go b/msg_unix_test.go
index 018e215..57e1547 100644
--- a/msg_unix_test.go
+++ b/msg_unix_test.go
@@ -120,28 +120,27 @@ func TestMsg_WriteToFile_unixOnly(t *testing.T) {
 	})
 }
 
-/*
-func TestMsg_WriteToTempFileFailed(t *testing.T) {
-	m := NewMsg()
-	_ = m.From("Toni Tester <tester@example.com>")
-	_ = m.To("Ellenor Tester <ellinor@example.com>")
-	m.SetBodyString(TypeTextPlain, "This is a test")
+func TestMsg_WriteToTempFile_unixOnly(t *testing.T) {
+	if os.Getenv("PERFORM_UNIX_OPEN_WRITE_TESTS") != "true" {
+		t.Skipf("PERFORM_UNIX_OPEN_WRITE_TESTS variable is not set. Skipping unix open/write tests")
+	}
 
-	curTmpDir := os.Getenv("TMPDIR")
-	defer func() {
-		if err := os.Setenv("TMPDIR", curTmpDir); err != nil {
-			t.Errorf("failed to set TMPDIR environment variable: %s", err)
+	t.Run("WriteToTempFile fails on invalid TMPDIR", func(t *testing.T) {
+		// We store the current TMPDIR variable so we can set it back when the test is over
+		curTmpDir := os.Getenv("TMPDIR")
+		t.Cleanup(func() {
+			if err := os.Setenv("TMPDIR", curTmpDir); err != nil {
+				t.Errorf("failed to set TMPDIR environment variable: %s", err)
+			}
+		})
+
+		if err := os.Setenv("TMPDIR", "/invalid/directory/that/does/not/exist"); err != nil {
+			t.Fatalf("failed to set TMPDIR environment variable: %s", err)
 		}
-	}()
-
-	if err := os.Setenv("TMPDIR", "/invalid/directory/that/does/not/exist"); err != nil {
-		t.Errorf("failed to set TMPDIR environment variable: %s", err)
-	}
-	_, err := m.WriteToTempFile()
-	if err == nil {
-		t.Errorf("WriteToTempFile() did not fail as expected")
-	}
+		message := testMessage(t)
+		_, err := message.WriteToTempFile()
+		if err == nil {
+			t.Errorf("expected writing to invalid TMPDIR to fail, got: %s", err)
+		}
+	})
 }
-
-
-*/