[ty] Migrate the namespace package module resolver tests to mdtests (#18133)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

crates/ty_python_semantic/resources/mdtest/import/namespace.md

@@ -0,0 +1,107 @@
+# Namespace package
+
+## Basic namespace package
+
+```toml
+[environment]
+python = "/.venv"
+```
+
+`parent/child/one.py`:
+
+```py
+one = 1
+```
+
+`/.venv/<path-to-site-packages>/parent/child/two.py`:
+
+```py
+two = 2
+```
+
+`main.py`:
+
+```py
+import parent.child.one
+import parent.child.two
+```
+
+`from.py`
+
+```py
+# TODO: This should not be an error
+from parent.child import one, two  # error: [unresolved-import]
+```
+
+## Regular package in namespace package
+
+```toml
+[environment]
+python = "/.venv"
+```
+
+An adapted test case from the
+[PEP420 examples](https://peps.python.org/pep-0420/#nested-namespace-packages). The
+`src/parent/child` package is a regular package. Therefore, `site_packages/parent/child/two.py`
+should not be resolved.
+
+```ignore
+src
+  parent
+    child
+      __init__.py
+      one.py
+.venv/site-packages
+  parent
+    child
+      two.py
+```
+
+`parent/child/__init__.py`:
+
+```py
+```
+
+`parent/child/one.py`:
+
+```py
+one = 1
+```
+
+`/.venv/<path-to-site-packages>/parent/child/two.py`:
+
+```py
+two = 2
+```
+
+`main.py`:
+
+```py
+import parent.child.one
+
+import parent.child.two  # error: [unresolved-import]
+```
+
+## Priority between file and identically named namespace package
+
+If there's a namespace package with the same name as a module, the module takes precedence.
+
+`foo.py`:
+
+```py
+x = "module"
+```
+
+`foo/bar.py`:
+
+```py
+x = "namespace"
+```
+
+```py
+from foo import x
+
+reveal_type(x)  # revealed: Unknown | Literal["module"]
+
+import foo.bar  # error: [unresolved-import]
+```

crates/ty_python_semantic/src/module_resolver/resolver.rs

@@ -1288,25 +1288,6 @@ mod tests {
         );
     }
 
-    #[test]
-    fn single_file_takes_priority_over_namespace_package() {
-        //const SRC: &[FileSpec] = &[("foo.py", "x = 1")];
-        const SRC: &[FileSpec] = &[("foo.py", "x = 1"), ("foo/bar.py", "x = 2")];
-
-        let TestCase { db, src, .. } = TestCaseBuilder::new().with_src_files(SRC).build();
-
-        let foo_module_name = ModuleName::new_static("foo").unwrap();
-        let foo_bar_module_name = ModuleName::new_static("foo.bar").unwrap();
-
-        // `foo.py` takes priority over the `foo` namespace package
-        let foo_module = resolve_module(&db, &foo_module_name).unwrap();
-        assert_eq!(foo_module.file().path(&db), &src.join("foo.py"));
-
-        // `foo.bar` isn't recognised as a module
-        let foo_bar_module = resolve_module(&db, &foo_bar_module_name);
-        assert_eq!(foo_bar_module, None);
-    }
-
     #[test]
     fn typing_stub_over_module() {
         const SRC: &[FileSpec] = &[("foo.py", "print('Hello, world!')"), ("foo.pyi", "x: int")];
@@ -1349,82 +1330,6 @@ mod tests {
         );
     }
 
-    #[test]
-    fn namespace_package() {
-        // From [PEP420](https://peps.python.org/pep-0420/#nested-namespace-packages).
-        // But uses `src` for `project1` and `site-packages` for `project2`.
-        // ```
-        // src
-        //   parent
-        //     child
-        //       one.py
-        // site_packages
-        //   parent
-        //     child
-        //       two.py
-        // ```
-        let TestCase {
-            db,
-            src,
-            site_packages,
-            ..
-        } = TestCaseBuilder::new()
-            .with_src_files(&[("parent/child/one.py", "print('Hello, world!')")])
-            .with_site_packages_files(&[("parent/child/two.py", "print('Hello, world!')")])
-            .build();
-
-        let one_module_name = ModuleName::new_static("parent.child.one").unwrap();
-        let one_module_path = FilePath::System(src.join("parent/child/one.py"));
-        assert_eq!(
-            resolve_module(&db, &one_module_name),
-            path_to_module(&db, &one_module_path)
-        );
-
-        let two_module_name = ModuleName::new_static("parent.child.two").unwrap();
-        let two_module_path = FilePath::System(site_packages.join("parent/child/two.py"));
-        assert_eq!(
-            resolve_module(&db, &two_module_name),
-            path_to_module(&db, &two_module_path)
-        );
-    }
-
-    #[test]
-    fn regular_package_in_namespace_package() {
-        // Adopted test case from the [PEP420 examples](https://peps.python.org/pep-0420/#nested-namespace-packages).
-        // The `src/parent/child` package is a regular package. Therefore, `site_packages/parent/child/two.py` should not be resolved.
-        // ```
-        // src
-        //   parent
-        //     child
-        //       one.py
-        // site_packages
-        //   parent
-        //     child
-        //       two.py
-        // ```
-        const SRC: &[FileSpec] = &[
-            ("parent/child/__init__.py", "print('Hello, world!')"),
-            ("parent/child/one.py", "print('Hello, world!')"),
-        ];
-
-        const SITE_PACKAGES: &[FileSpec] = &[("parent/child/two.py", "print('Hello, world!')")];
-
-        let TestCase { db, src, .. } = TestCaseBuilder::new()
-            .with_src_files(SRC)
-            .with_site_packages_files(SITE_PACKAGES)
-            .build();
-
-        let one_module_path = FilePath::System(src.join("parent/child/one.py"));
-        let one_module_name =
-            resolve_module(&db, &ModuleName::new_static("parent.child.one").unwrap());
-        assert_eq!(one_module_name, path_to_module(&db, &one_module_path));
-
-        assert_eq!(
-            None,
-            resolve_module(&db, &ModuleName::new_static("parent.child.two").unwrap())
-        );
-    }
-
     #[test]
     fn module_search_path_priority() {
         let TestCase {