Add test for rejecting pyproject.toml with empty build-system table

tests/data/src/pep518_invalid_build_system/MANIFEST.in

@@ -0,0 +1 @@
+include pyproject.toml

tests/data/src/pep518_invalid_build_system/pep518.py

@@ -0,0 +1 @@
+#dummy

tests/data/src/pep518_invalid_build_system/pyproject.toml

@@ -0,0 +1,2 @@
+[build-system]
+# This table is intentionally empty.

tests/data/src/pep518_invalid_build_system/setup.py

@@ -0,0 +1,8 @@
+#!/usr/bin/env python
+from setuptools import setup
+
+setup(
+    name='pep518_invalid_build_system',
+    version='1.0.0',
+    py_modules=['pep518'],
+)

tests/functional/test_install.py

@@ -47,6 +47,16 @@ def test_pep518_refuses_invalid_requires(script, data, common_wheels):
     assert "does not comply with PEP 518" in result.stderr
 
 
+def test_pep518_refuses_invalid_build_system(script, data, common_wheels):
+    result = script.pip(
+        'install', '-f', common_wheels,
+        data.src.join("pep518_invalid_build_system"),
+        expect_error=True
+    )
+    assert result.returncode == 1
+    assert "does not comply with PEP 518" in result.stderr
+
+
 def test_pep518_allows_missing_requires(script, data, common_wheels):
     result = script.pip(
         'install', '-f', common_wheels,