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

2 files changed, 217 insertions, 0 deletions

diff --git a/tests/builder/diagnose.test.py b/tests/builder/diagnose.test.py
new file mode 100644
index 0000000..c61b3a9
--- /dev/null
+++ b/tests/builder/diagnose.test.py
@@ -0,0 +1,105 @@
+"""Tests for the diagnostic helpers in :mod:`edify.builder.diagnose`."""
+
+from types import SimpleNamespace
+
+import pytest
+
+from edify import Pattern, RegexBuilder
+from edify.builder.diagnose import _fallback, _frame_display_name, diagnose_unfinished
+from edify.errors.comparison import CannotCompareUnfinishedBuilderError
+
+
+def _first_pointer_hint(text: str) -> str | None:
+    for line in text.splitlines():
+        if "->" in line and ".py:" in line:
+            return line
+    return None
+
+
+def test_diagnose_returns_none_when_state_is_fully_specified():
+    finished = RegexBuilder().digit()
+    problem = diagnose_unfinished(finished._state, "left operand")
+    assert problem is None
+
+
+def test_open_group_frame_names_group_in_the_problem_description():
+    unfinished = RegexBuilder().group().digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert "open `group()`" in text
+
+
+def test_open_capture_frame_names_capture_in_the_problem_description():
+    unfinished = RegexBuilder().capture().digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert "open `capture()`" in text
+
+
+def test_open_named_capture_frame_names_the_name_in_the_problem_description():
+    unfinished = RegexBuilder().named_capture("year").digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert 'named_capture("year")' in text
+
+
+def test_open_assert_ahead_frame_names_lookahead():
+    unfinished = RegexBuilder().assert_ahead().digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert "assert_ahead()" in text
+
+
+def test_open_assert_not_ahead_frame_names_negative_lookahead():
+    unfinished = RegexBuilder().assert_not_ahead().digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert "assert_not_ahead()" in text
+
+
+def test_open_assert_behind_frame_names_lookbehind():
+    unfinished = RegexBuilder().assert_behind().digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert "assert_behind()" in text
+
+
+def test_open_assert_not_behind_frame_names_negative_lookbehind():
+    unfinished = RegexBuilder().assert_not_behind().digit()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished == RegexBuilder()
+    text = str(excinfo.value)
+    assert "assert_not_behind()" in text
+
+
+def test_frame_display_name_falls_back_to_class_name_for_unknown_container():
+    mystery_class = type("MysteryContainer", (), {})
+    mystery_element = mystery_class()
+    fake_frame = SimpleNamespace(type_node=mystery_element)
+    assert _frame_display_name(fake_frame) == "MysteryContainer"
+
+
+def test_fallback_returns_context_when_provided():
+    dummy_context = "sentinel"
+    assert _fallback(dummy_context) == "sentinel"
+
+
+def test_fallback_returns_placeholder_when_context_is_none():
+    placeholder = _fallback(None)
+    assert placeholder.filename == "<unknown>"
+    assert placeholder.lineno == 0
+    assert placeholder.source_line == ""
+
+
+def test_dangling_quantifier_on_pattern_reports_quantifier_name():
+    unfinished_pattern = Pattern().one_or_more()
+    with pytest.raises(CannotCompareUnfinishedBuilderError) as excinfo:
+        _ = unfinished_pattern == Pattern()
+    text = str(excinfo.value)
+    assert "pending `.one_or_more()`" in text
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"