Integration test to reproduce

src/incremental/tests/test_pyproject.py

@@ -49,14 +49,24 @@ def test_fileNotFound(self):
         path = os.path.join(cast(str, self.mktemp()), "pyproject.toml")
         self.assertIsNone(_load_pyproject_toml(path))
 
-    def test_nameMissing(self):
+    def test_configMissing(self):
         """
-        `ValueError` is raised when ``[tool.incremental]`` is present but
-        he project name isn't available.
+        A ``pyproject.toml`` that exists but provides no relevant configuration
+        is ignored.
         """
         for toml in [
             "\n",
             "[tool.notincremental]\n",
+            "[project]\n",
+        ]:
+            self.assertIsNone(self._loadToml(toml))
+
+    def test_nameMissing(self):
+        """
+        `ValueError` is raised when ``[tool.incremental]`` is present but
+        the project name isn't available.
+        """
+        for toml in [
             "[tool.incremental]\n",
             "[project]\n[tool.incremental]\n",
         ]:

tests/example_noop/pyproject.toml

@@ -0,0 +1,3 @@
+# This file exists, but doesn't contain any [project] or
+# [tool.incremental] configuration so Incremental ignores it.
+[tool.something]

tests/example_noop/setup.py

@@ -0,0 +1,13 @@
+from setuptools import setup
+
+setup(
+    name="example_noop",
+    version="100",
+    packages=["example_noop"],
+    zip_safe=False,
+    setup_requires=[
+        # Ensure Incremental is installed for test purposes
+        # (but it won't do anything).
+        "incremental",
+    ],
+)

tests/example_noop/src/example_noop/__init__.py

@@ -0,0 +1,11 @@
+"""
+An example setuptools project that doesn't use Incremental at all.
+
+This is used to verify that Incremental correctly deactivates itself
+when there is no opt-in, even though setuptools always invokes its
+hook.
+"""
+
+__version__ = "100"
+
+__all__ = ["__version__"]

tests/test_examples.py

@@ -97,3 +97,15 @@ def test_hatch_version_set(self):
             # Hatch may wrap the output, so we are flexible about the specifics of whitespace.
             suggestion.replace(b".", rb"\.").replace(b" ", b"\\s+"),
         )
+
+    def test_noop(self):
+        """
+        The Incremental setuptools hook is a silent no-op when there is no Incremental
+        configuration to be found.
+        """
+        build_and_install(TEST_DIR.child("example_noop"))
+
+        import example_noop
+
+        self.assertEqual(example_noop.__version__, "100")
+        self.assertEqual(metadata.version("example_noop"), "100")