1 files changed, 474 insertions, 0 deletions
diff --git a/tests/unit/test_exceptions.py b/tests/unit/test_exceptions.py
new file mode 100644
index 000000000..8f8224dc8
--- /dev/null
+++ b/tests/unit/test_exceptions.py
@@ -0,0 +1,474 @@
+"""Tests the presentation style of exceptions."""
+
+import io
+import textwrap
+
+import pytest
+from pip._vendor import rich
+
+from pip._internal.exceptions import DiagnosticPipError
+
+
+class TestDiagnosticPipErrorCreation:
+    def test_fails_without_reference(self) -> None:
+        class DerivedError(DiagnosticPipError):
+            pass
+
+        with pytest.raises(AssertionError) as exc_info:
+            DerivedError(message="", context=None, hint_stmt=None)
+
+        assert str(exc_info.value) == "error reference not provided!"
+
+    def test_can_fetch_reference_from_subclass(self) -> None:
+        class DerivedError(DiagnosticPipError):
+            reference = "subclass-reference"
+
+        obj = DerivedError(message="", context=None, hint_stmt=None)
+        assert obj.reference == "subclass-reference"
+
+    def test_can_fetch_reference_from_arguments(self) -> None:
+        class DerivedError(DiagnosticPipError):
+            pass
+
+        obj = DerivedError(
+            message="", context=None, hint_stmt=None, reference="subclass-reference"
+        )
+        assert obj.reference == "subclass-reference"
+
+    @pytest.mark.parametrize(
+        "name",
+        [
+            "BADNAME",
+            "BadName",
+            "bad_name",
+            "BAD_NAME",
+            "_bad",
+            "bad-name-",
+            "bad--name",
+            "-bad-name",
+            "bad-name-due-to-1-number",
+        ],
+    )
+    def test_rejects_non_kebab_case_names(self, name: str) -> None:
+        class DerivedError(DiagnosticPipError):
+            reference = name
+
+        with pytest.raises(AssertionError) as exc_info:
+            DerivedError(message="", context=None, hint_stmt=None)
+
+        assert str(exc_info.value) == "error reference must be kebab-case!"
+
+
+def rendered_in_ascii(error: DiagnosticPipError, *, color: bool = False) -> str:
+    with io.BytesIO() as stream:
+        console = rich.console.Console(
+            force_terminal=False,
+            file=io.TextIOWrapper(stream, encoding="ascii", newline=""),
+            color_system="truecolor" if color else None,
+        )
+        console.print(error)
+        return stream.getvalue().decode("ascii")
+
+
+class TestDiagnosticPipErrorPresentation_ASCII:
+    def test_complete(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            Something went wrong
+            very wrong.
+
+            note: You did something wrong, which is what caused this error.
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_complete_color(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke.",
+            context="Something went wrong\nvery wrong.",
+            note_stmt="You did something wrong.",
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        def esc(code: str = "0") -> str:
+            return f"\x1b[{code}m"
+
+        assert rendered_in_ascii(err, color=True) == textwrap.dedent(
+            f"""\
+            {esc("1;31")}error{esc("0")}: {esc("1")}test-diagnostic{esc("0")}
+
+            Oh no!
+            It broke.
+
+            Something went wrong
+            very wrong.
+
+            {esc("1;35")}note{esc("0")}: You did something wrong.
+            {esc("1;36")}hint{esc("0")}: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_context(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            note: You did something wrong, which is what caused this error.
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_note(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt=None,
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            Something went wrong
+            very wrong.
+
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_hint(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt=None,
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            Something went wrong
+            very wrong.
+
+            note: You did something wrong, which is what caused this error.
+            """
+        )
+
+    def test_no_context_no_hint(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt=None,
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            note: You did something wrong, which is what caused this error.
+            """
+        )
+
+    def test_no_context_no_note(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            note_stmt=None,
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_hint_no_note(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt=None,
+            hint_stmt=None,
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+
+            Something went wrong
+            very wrong.
+            """
+        )
+
+    def test_no_hint_no_note_no_context(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            hint_stmt=None,
+            note_stmt=None,
+        )
+
+        assert rendered_in_ascii(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            Oh no!
+            It broke. :(
+            """
+        )
+
+
+def rendered(error: DiagnosticPipError, *, color: bool = False) -> str:
+    with io.StringIO() as stream:
+        console = rich.console.Console(
+            force_terminal=False,
+            file=stream,
+            color_system="truecolor" if color else None,
+        )
+        console.print(error)
+        return stream.getvalue()
+
+
+class TestDiagnosticPipErrorPresentation_Unicode:
+    def test_complete(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+            │ It broke. :(
+            ╰─> Something went wrong
+                very wrong.
+
+            note: You did something wrong, which is what caused this error.
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_complete_color(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke.",
+            context="Something went wrong\nvery wrong.",
+            note_stmt="You did something wrong.",
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        def esc(code: str = "0") -> str:
+            return f"\x1b[{code}m"
+
+        assert rendered(err, color=True) == textwrap.dedent(
+            f"""\
+            {esc("1;31")}error{esc("0")}: {esc("1")}test-diagnostic{esc("0")}
+
+            {esc("31")}×{esc("0")} Oh no!
+            {esc("31")}│{esc("0")} It broke.
+            {esc("31")}╰─>{esc("0")} Something went wrong
+            {esc("31")}   {esc("0")} very wrong.
+
+            {esc("1;35")}note{esc("0")}: You did something wrong.
+            {esc("1;36")}hint{esc("0")}: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_context(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+              It broke. :(
+
+            note: You did something wrong, which is what caused this error.
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_note(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt=None,
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+            │ It broke. :(
+            ╰─> Something went wrong
+                very wrong.
+
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_hint(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt=None,
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+            │ It broke. :(
+            ╰─> Something went wrong
+                very wrong.
+
+            note: You did something wrong, which is what caused this error.
+            """
+        )
+
+    def test_no_context_no_hint(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            note_stmt="You did something wrong, which is what caused this error.",
+            hint_stmt=None,
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+              It broke. :(
+
+            note: You did something wrong, which is what caused this error.
+            """
+        )
+
+    def test_no_context_no_note(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            note_stmt=None,
+            hint_stmt="Do it better next time, by trying harder.",
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+              It broke. :(
+
+            hint: Do it better next time, by trying harder.
+            """
+        )
+
+    def test_no_hint_no_note(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context="Something went wrong\nvery wrong.",
+            note_stmt=None,
+            hint_stmt=None,
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+            │ It broke. :(
+            ╰─> Something went wrong
+                very wrong.
+            """
+        )
+
+    def test_no_hint_no_note_no_context(self) -> None:
+        err = DiagnosticPipError(
+            reference="test-diagnostic",
+            message="Oh no!\nIt broke. :(",
+            context=None,
+            hint_stmt=None,
+            note_stmt=None,
+        )
+
+        assert rendered(err) == textwrap.dedent(
+            """\
+            error: test-diagnostic
+
+            × Oh no!
+              It broke. :(
+            """
+        )