add test coverage for non-Windows platforms

crates/tests/linux/tests/hresult.rs

@@ -0,0 +1,34 @@
+// This tests code paths in `windows-result` that are different on non-Windows platforms.
+#![cfg(not(windows))]
+
+use windows::core::Error;
+use windows::Win32::Foundation::{E_FAIL, S_OK};
+
+#[test]
+fn basic_hresult() {
+    assert!(E_FAIL.is_err());
+    assert!(S_OK.is_ok());
+
+    let ok_message = S_OK.message();
+    assert_eq!(ok_message, "0x00000000");
+}
+
+#[test]
+fn error_message_is_not_supported() {
+    let e = Error::new(S_OK, "this gets ignored");
+    let message = e.message();
+    assert_eq!(message, "0x00000000");
+}
+
+#[test]
+#[should_panic]
+fn from_win32_panics() {
+    // from_win32() is not implemented on non-Windows platforms.
+    let _e = Error::from_win32();
+}
+
+#[test]
+fn error_from_hresult() {
+    let e = Error::from(E_FAIL);
+    assert_eq!(e.code(), E_FAIL);
+}