fix(lib): allow DocTest to discover methods from subclasses of eqx.Module

Closes #1016.

In the end, there were two issues: (1) `DocTestFinder._from_module` was returning `False` because the `__module__` attribute was not correct, and (2) the documentation was not copied to the wrapper class so doctests could not be discovered.

My solution is inspired from what Python is doing with their own decorators, see https://github.com/python/cpython/blob/4617d68d73409e83d6ab31106d10421d44048787/Lib/functools.py#L1033-L1049

Author: jeertmans

equinox/_module.py

@@ -681,6 +681,15 @@ def __init__(self, method):
         if getattr(self.method, "__isabstractmethod__", False):
             self.__isabstractmethod__ = self.method.__isabstractmethod__
 
+    # Fixes https://github.com/patrick-kidger/equinox/issues/1016
+    @property
+    def __module__(self):
+        return self.method.__module__
+
+    @property
+    def __doc__(self):
+        return self.method.__doc__
+
     def __get__(self, instance, owner):
         del owner
         if instance is None:

tests/test_module.py

@@ -1,5 +1,6 @@
 import abc
 import dataclasses
+import doctest
 import functools as ft
 import inspect
 import pickle
@@ -1257,3 +1258,61 @@ def test_tree_roundtrip_serialise_roundtrip():
     x = pickle.loads(pickle.dumps(x))
     tree2 = jtu.tree_structure(x)
     assert tree == tree2
+
+
+# https://github.com/patrick-kidger/equinox/issues/1016
+def test_doctest():
+    class Example(eqx.Module):
+        def foo(self) -> int:
+            """
+            >>> example = Example()
+            >>> example.foo()
+            1
+            """
+            return 1
+
+        @property
+        def bar(self) -> int:
+            """
+            >>> example = Example()
+            >>> example.bar
+            1
+            """
+            return 1
+
+        @classmethod
+        def baz(self) -> int:
+            """
+            >>> Example.baz()
+            1
+            """
+            return 1
+
+        @eqx.filter_jit
+        def biz(self) -> int:
+            """
+            >>> example = Example()
+            >>> example.biz()
+            1
+            """
+            return 1
+
+        @staticmethod
+        def buz() -> int:
+            """
+            >>> example = Example()
+            >>> example.buz()
+            1
+            """
+            return 1
+
+    tests = doctest.DocTestFinder().find(Example)
+    tests = [test for test in tests if test.examples]
+
+    assert len(tests) == 5
+
+    assert any("foo" in str(test) for test in tests)
+    assert any("bar" in str(test) for test in tests)
+    assert any("baz" in str(test) for test in tests)
+    assert any("biz" in str(test) for test in tests)
+    assert any("buz" in str(test) for test in tests)