test: cover diagnose fallback branches and caller-context position fallbacks

1 files changed, 112 insertions, 0 deletions

diff --git a/tests/errors/context.test.py b/tests/errors/context.test.py
new file mode 100644
index 0000000..3b54605
--- /dev/null
+++ b/tests/errors/context.test.py
@@ -0,0 +1,112 @@
+"""Tests for the caller-source-location capture helpers in :mod:`edify.errors.context`."""
+
+from types import SimpleNamespace
+from unittest import mock
+
+from edify.errors.context import (
+    CallerContext,
+    _context_for_frame,
+    capture_caller_context,
+)
+
+
+class _FakeCode:
+    """A stand-in for ``types.CodeType`` used to force specific ``co_positions`` behaviour."""
+
+    def __init__(self, filename: str, positions: list[tuple]) -> None:
+        self.co_filename = filename
+        self._positions = list(positions)
+
+    def co_positions(self):
+        return iter(self._positions)
+
+
+class _FakeFrame:
+    """A stand-in for ``types.FrameType`` shaped for :func:`_context_for_frame`."""
+
+    def __init__(
+        self,
+        filename: str,
+        f_lineno: int,
+        f_lasti: int,
+        positions: list[tuple],
+    ) -> None:
+        self.f_code = _FakeCode(filename, positions)
+        self.f_lineno = f_lineno
+        self.f_lasti = f_lasti
+
+
+def test_capture_caller_context_returns_none_when_every_frame_is_inside_edify():
+    with mock.patch(
+        "edify.errors.context.sys._getframe", return_value=None
+    ):
+        assert capture_caller_context() is None
+
+
+def test_context_for_frame_uses_lineno_fallback_when_instruction_index_out_of_range():
+    frame = _FakeFrame(
+        filename="/tmp/fake.py",
+        f_lineno=42,
+        f_lasti=999,
+        positions=[],
+    )
+    context = _context_for_frame(frame)
+    assert context.lineno == 42
+    assert context.colno == 1
+    assert context.end_colno == 1
+
+
+def test_context_for_frame_defaults_start_line_when_position_start_line_is_none():
+    frame = _FakeFrame(
+        filename="/tmp/fake.py",
+        f_lineno=99,
+        f_lasti=0,
+        positions=[(None, None, None, None)],
+    )
+    context = _context_for_frame(frame)
+    assert context.lineno == 99
+
+
+def test_context_for_frame_defaults_end_line_when_position_end_line_is_none():
+    frame = _FakeFrame(
+        filename="/tmp/fake.py",
+        f_lineno=7,
+        f_lasti=0,
+        positions=[(5, None, 2, 4)],
+    )
+    context = _context_for_frame(frame)
+    assert context.lineno == 5
+    assert context.colno == 3
+    assert context.end_colno == 5
+
+
+def test_context_for_frame_defaults_start_col_when_position_start_col_is_none():
+    frame = _FakeFrame(
+        filename="/tmp/fake.py",
+        f_lineno=1,
+        f_lasti=0,
+        positions=[(1, 1, None, 5)],
+    )
+    context = _context_for_frame(frame)
+    assert context.colno == 1
+    assert context.end_colno == 6
+
+
+def test_context_for_frame_defaults_end_col_when_position_end_col_is_none():
+    frame = _FakeFrame(
+        filename="/tmp/fake.py",
+        f_lineno=1,
+        f_lasti=0,
+        positions=[(1, 1, 3, None)],
+    )
+    context = _context_for_frame(frame)
+    assert context.colno == 4
+    assert context.end_colno == 4
+
+
+def test_caller_context_dataclass_is_frozen_and_holds_all_five_fields():
+    context = CallerContext(
+        filename="a.py", lineno=1, colno=1, end_colno=5, source_line="x = 1"
+    )
+    assert context.filename == "a.py"
+    assert context.source_line == "x = 1"