Add test for cross-module usages

test/test_api/import_tree_for_usages/__init__.py

@@ -0,0 +1,4 @@
+"""
+An import tree, for testing usages.
+"""
+

test/test_api/import_tree_for_usages/a.py

@@ -0,0 +1,4 @@
+from . import b
+
+def foo():
+    b.bar()

test/test_api/import_tree_for_usages/b.py

@@ -0,0 +1,2 @@
+def bar():
+    pass

test/test_api/test_usages.py

@@ -1,6 +1,48 @@
 import jedi
-
+import os.path
 
 def test_import_usage():
     s = jedi.Script("from .. import foo", line=1, column=18, path="foo.py")
     assert [usage.line for usage in s.usages()] == [1]
+
+
+def usages_with_additional_modules(script, additional_modules):
+    """
+    Stripped down version of `jedi.api.Script.usages` that can take an
+    explicit set of additional modules. For use with `test_cross_module_usages`.
+    """
+
+    definition_names = jedi.api.usages.resolve_potential_imports(script._evaluator,
+                                                        script._goto())
+    modules = set([d.get_root_context() for d in definition_names])
+    modules.add(script._get_module())
+    for additional_module in additional_modules:
+        modules.add(additional_module._name.get_root_context())
+    return jedi.api.usages.usages(script._evaluator, definition_names, modules)
+
+
+def test_cross_module_usages():
+    """
+    This tests finding of usages between different modules. In
+    `jedi.api.usages.compare_contexts`, this exercises the case where
+    `c1 != c2`. This tests whether `jedi` can find the usage of
+    `import_tree_for_usages.b.bar` in `import_tree_for_usages.a`
+    """
+
+    def usages_script():
+        source = 'import import_tree_for_usages.b; import_tree_for_usages.b.bar'
+        return jedi.api.Script(source=source, line=1, column=len(source),
+                               sys_path=[os.path.dirname(os.path.abspath(__file__))])
+
+    def module_script():
+        source = 'import import_tree_for_usages.a; import_tree_for_usages.a'
+        return jedi.api.Script(source=source, line=1, column=len(source),
+                               sys_path=[os.path.dirname(os.path.abspath(__file__))])
+
+    module = module_script().goto_definitions()[0]
+    module_definition = module._name.get_root_context()
+    usages_list = usages_with_additional_modules(usages_script(), set([module]))
+
+    assert any([elt for elt in usages_list if elt.module_name == 'a']), (
+        "Did not find cross-module usage of :func:`b.bar` in :mod:`a`. Usages list was: {}"
+        .format(usages_list))