test: add snapshot test of macro expansion

Cargo.toml

@@ -32,3 +32,4 @@ indexmap = { version = "2.0.0", optional = true }
 
 [dev-dependencies]
 thiserror = "1.0"
+macrotest = { git = "https://github.com/antalsz/macrotest.git", branch = "optional-dependencies" }

tests/tests.rs

@@ -0,0 +1,45 @@
+use pyo3::{types::PyModule, PyResult, Python};
+
+// The code being tested is in a separate module so it can be expanded (see
+// [`test_macro_expansion`]) without expanding the contents of the tests
+// themselves.  This file must be in a subdirectory (`wrapper_tests/mod.rs`
+// instead of `wrapper_tests.rs`) because the generated `.expanded.rs` file
+// cannot be in the root `tests/` directory or `cargo test` will attempt to
+// build it as a test case as well.
+mod wrapper_tests;
+
+#[test]
+fn test_enum_as_data_struct_member() {
+    wrapper_tests::append_to_inittab();
+    pyo3::prepare_freethreaded_python();
+    let result: PyResult<()> = Python::with_gil(|py| {
+        let code = r#"
+from wrapper_tests import TestEnumUnaliased, TestEnumAliased, TestStruct, TestUnionEnum
+
+struct = TestStruct()
+
+assert struct.test_enum_unaliased == TestEnumUnaliased.One
+assert struct.test_enum_aliased == TestEnumAliased.NONE
+
+struct.test_enum_unaliased = TestEnumUnaliased.Two
+struct.test_enum_aliased = TestEnumAliased.Two
+
+assert struct.test_enum_unaliased == TestEnumUnaliased.Two
+assert struct.test_enum_aliased == TestEnumAliased.Two
+
+assert TestUnionEnum.new_unit().is_unit()
+"#;
+        PyModule::from_code(py, code, "example.py", "example")?;
+
+        Ok(())
+    });
+
+    result.expect("python code should execute without issue")
+}
+
+#[test]
+fn test_macro_expansion() {
+    // To regenerate the snapshot, delete the generated
+    // `tests/wrapper_tests/mod.expanded.rs` file and retun the test.
+    macrotest::expand("tests/wrapper_tests/mod.rs")
+}