1 files changed, 59 insertions, 26 deletions

diff --git a/tests/unit/test_pep517.py b/tests/unit/test_pep517.py
index 18cb178bb..5eefbf4e7 100644
--- a/tests/unit/test_pep517.py
+++ b/tests/unit/test_pep517.py
@@ -1,38 +1,63 @@
+import os
+from pathlib import Path
 from textwrap import dedent
 
 import pytest
 
-from pip._internal.exceptions import InstallationError
+from pip._internal.exceptions import InstallationError, InvalidPyProjectBuildRequires
 from pip._internal.req import InstallRequirement
+from tests.lib import TestData
 
 
-@pytest.mark.parametrize(('source', 'expected'), [
-    ("pep517_setup_and_pyproject", True),
-    ("pep517_setup_only", False),
-    ("pep517_pyproject_only", True),
-])
-def test_use_pep517(shared_data, source, expected):
+@pytest.mark.parametrize(
+    ("source", "expected"),
+    [
+        ("pep517_setup_and_pyproject", True),
+        ("pep517_setup_only", False),
+        ("pep517_pyproject_only", True),
+    ],
+)
+def test_use_pep517(shared_data: TestData, source: str, expected: bool) -> None:
     """
     Test that we choose correctly between PEP 517 and legacy code paths
     """
     src = shared_data.src.joinpath(source)
     req = InstallRequirement(None, None)
-    req.source_dir = src  # make req believe it has been unpacked
+    req.source_dir = os.fspath(src)  # make req believe it has been unpacked
     req.load_pyproject_toml()
     assert req.use_pep517 is expected
 
 
-@pytest.mark.parametrize(('source', 'msg'), [
-    ("pep517_setup_and_pyproject", "specifies a build backend"),
-    ("pep517_pyproject_only", "does not have a setup.py"),
-])
-def test_disabling_pep517_invalid(shared_data, source, msg):
+def test_use_pep517_rejects_setup_cfg_only(shared_data: TestData) -> None:
+    """
+    Test that projects with setup.cfg but no pyproject.toml are rejected.
+    """
+    src = shared_data.src.joinpath("pep517_setup_cfg_only")
+    req = InstallRequirement(None, None)
+    req.source_dir = os.fspath(src)  # make req believe it has been unpacked
+    with pytest.raises(InstallationError) as e:
+        req.load_pyproject_toml()
+    err_msg = e.value.args[0]
+    assert (
+        "does not appear to be a Python project: "
+        "neither 'setup.py' nor 'pyproject.toml' found" in err_msg
+    )
+
+
+@pytest.mark.parametrize(
+    ("source", "msg"),
+    [
+        ("pep517_setup_and_pyproject", "specifies a build backend"),
+        ("pep517_pyproject_only", "does not have a setup.py"),
+    ],
+)
+def test_disabling_pep517_invalid(shared_data: TestData, source: str, msg: str) -> None:
     """
     Test that we fail if we try to disable PEP 517 when it's not acceptable
     """
     src = shared_data.src.joinpath(source)
     req = InstallRequirement(None, None)
-    req.source_dir = src  # make req believe it has been unpacked
+    req.source_dir = os.fspath(src)  # make req believe it has been unpacked
 
     # Simulate --no-use-pep517
     req.use_pep517 = False
@@ -48,19 +73,27 @@ def test_disabling_pep517_invalid(shared_data, source, msg):
 @pytest.mark.parametrize(
     ("spec",), [("./foo",), ("git+https://example.com/pkg@dev#egg=myproj",)]
 )
-def test_pep517_parsing_checks_requirements(tmpdir, spec):
-    tmpdir.joinpath("pyproject.toml").write_text(dedent(
-        """
-        [build-system]
-        requires = [{!r}]
-        build-backend = "foo"
-        """.format(spec)
-    ))
+def test_pep517_parsing_checks_requirements(tmpdir: Path, spec: str) -> None:
+    tmpdir.joinpath("pyproject.toml").write_text(
+        dedent(
+            f"""
+            [build-system]
+            requires = [{spec!r}]
+            build-backend = "foo"
+            """
+        )
+    )
     req = InstallRequirement(None, None)
-    req.source_dir = tmpdir  # make req believe it has been unpacked
+    req.source_dir = os.fspath(tmpdir)  # make req believe it has been unpacked
 
-    with pytest.raises(InstallationError) as e:
+    with pytest.raises(InvalidPyProjectBuildRequires) as e:
         req.load_pyproject_toml()
 
-    err_msg = e.value.args[0]
-    assert "contains an invalid requirement" in err_msg
+    error = e.value
+
+    assert str(req) in error.message
+    assert error.context
+    assert "build-system.requires" in error.context
+    assert "contains an invalid requirement" in error.context
+    assert error.hint_stmt
+    assert "PEP 518" in error.hint_stmt