test: move test code into a separate module

This enables easier manual testing with `cargo expand`, and will enable easier
snapshot testing later.

tests/tests.rs

@@ -0,0 +1,38 @@
+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")
+}

tests/wrapper_tests.rs → tests/wrapper_tests/mod.rs

@@ -77,31 +77,6 @@ fn wrapper_tests(py: Python<'_>, m: &PyModule) -> PyResult<()> {
     python::init_submodule("wrapper_tests", py, m)
 }
 
-#[test]
-fn test_enum_as_data_struct_member() {
+pub fn append_to_inittab() {
     pyo3::append_to_inittab!(wrapper_tests);
-    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")
 }