test: cover string-formatting and representation helpers

Add a dedicated test module exercising the previously-uncovered
string-formatting paths in injector:

- UnsatisfiedRequirement.__str__ (with and without an owner)
- _describe (named objects, tuple/list, and the str() fallback)
- _get_origin normalization of typing.List/typing.Dict aliases

Kept separate from injector_test.py to avoid polluting the functional
suite with coverage-driven edge cases.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Author: KrzysztofMadejski

injector_100_percent_coverage_test.py

@@ -0,0 +1,61 @@
+"""Targeted tests that exercise the remaining uncovered lines in ``injector``.
+
+These cases don't fit naturally into the functional test suite in
+``injector_test.py`` – they poke at internal string-formatting helpers and
+rarely-hit edge-case/error branches purely to drive coverage to 100%.
+"""
+
+from typing import Dict, List
+
+import injector
+from injector import UnsatisfiedRequirement
+
+
+# --- String / representation formatting --------------------------------------
+
+
+def test_unsatisfied_requirement_str_without_owner():
+    # The ``self.owner`` falsy branch of ``UnsatisfiedRequirement.__str__``.
+    error = UnsatisfiedRequirement(None, int)
+    assert str(error) == 'unsatisfied requirement on int'
+
+
+def test_unsatisfied_requirement_str_with_owner():
+    # The ``self.owner`` truthy branch, which prepends a description of the owner.
+    class Owner:
+        pass
+
+    owner = Owner()
+    error = UnsatisfiedRequirement(owner, int)
+    message = str(error)
+    assert message.endswith('has an unsatisfied requirement on int')
+    assert message != 'unsatisfied requirement on int'
+
+
+def test_describe_named_object():
+    # Objects exposing ``__name__`` are described by that name.
+    assert injector._describe(int) == 'int'
+
+
+def test_describe_tuple_uses_first_element():
+    # Tuples/lists are described via their first element's ``__name__``.
+    assert injector._describe((int,)) == '[int]'
+    assert injector._describe([str]) == '[str]'
+
+
+def test_describe_falls_back_to_str():
+    # Anything without ``__name__`` that isn't a tuple/list falls back to ``str``.
+    assert injector._describe(123) == '123'
+
+
+def test_get_origin_normalizes_typing_aliases():
+    # Some (older) typings store ``typing.List``/``typing.Dict`` as ``__origin__``;
+    # ``_get_origin`` normalizes those back to the builtin containers.
+    class FakeListAlias:
+        __origin__ = List
+
+    class FakeDictAlias:
+        __origin__ = Dict
+
+    assert injector._get_origin(FakeListAlias) is list
+    assert injector._get_origin(FakeDictAlias) is dict