feat(crc32c): add unit and cover nox sessions

packages/google-crc32c/.coveragerc

@@ -17,12 +17,18 @@
 # Generated by synthtool. DO NOT EDIT!
 [run]
 branch = True
+source =
+  src/google_crc32c
 omit =
   google/__init__.py
   google/cloud/__init__.py
+  # Windows-only DLL bootstrap logic (not executed on Linux/macOS)
+  src/google_crc32c/__config__.py
+  # Uncompiled C extension wrapper (exercised in wheel check session, not pure-Python unit tests)
+  src/google_crc32c/cext.py
 
 [report]
-fail_under = 0
+fail_under = 100
 show_missing = True
 exclude_lines =
     # Re-enable the standard pragma
@@ -37,3 +43,7 @@ omit =
   */core/*.py
   */site-packages/*.py
   google/cloud/__init__.py
+  # Windows-only DLL bootstrap logic (not executed on Linux/macOS)
+  src/google_crc32c/__config__.py
+  # Uncompiled C extension wrapper (exercised in wheel check session, not pure-Python unit tests)
+  src/google_crc32c/cext.py

packages/google-crc32c/noxfile.py

@@ -40,6 +40,7 @@
     "blacken",
     "format",
     "lint_setup_py",
+    "cover",
     "mypy",
     "prerelease_deps",
     "core_deps_from_source",
@@ -66,11 +67,13 @@ def build_libcrc32c(session):
 
 @nox.session(python=UNIT_TEST_PYTHON_VERSIONS)
 def check(session):
-    session.install("pytest")
+    session.install("pytest", "pytest-cov")
     session.install("--no-index", f"--find-links={HERE}/wheels", "google-crc32c")
 
     # Run py.test against the unit tests.
-    session.run("py.test", "tests")
+    session.run(
+        "pytest", "--cov=google_crc32c", "--cov=tests", "tests", *session.posargs
+    )
     session.run("python", f"{HERE}/scripts/check_crc32c_extension.py", *session.posargs)
 
 
@@ -174,25 +177,40 @@ def lint_setup_py(session):
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def prerelease_deps(session):
     """Run all tests with prerelease versions of dependencies installed."""
-    # TODO(https://github.com/googleapis/google-cloud-python/issues/16014):
-    # Add prerelease deps tests
-    session.skip("prerelease deps tests are not yet supported")
+    session.skip(
+        "prerelease_deps session is not applicable as google-crc32c has no runtime dependencies"
+    )
 
 
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def core_deps_from_source(session):
     """Run all tests with core dependencies installed from source
     rather than pulling the dependencies from PyPI.
     """
-    # TODO(https://github.com/googleapis/google-cloud-python/issues/16014):
-    # Add core deps from source tests
-    session.skip("Core deps from source tests are not yet supported")
+    session.skip(
+        "core_deps_from_source session is not applicable as google-crc32c has no core dependencies"
+    )
 
 
-@nox.session(python=ALL_PYTHON)
+@nox.session(python=UNIT_TEST_PYTHON_VERSIONS)
 def unit(session):
     """Run all unit tests."""
-    session.skip("Unit tests are not supported")
+    session.env["CRC32C_PURE_PYTHON"] = "1"
+    session.env["PYTHONPATH"] = "src"
+    session.install("pytest", "pytest-cov")
+    session.run("pytest", "--cov=src/google_crc32c", "tests", *session.posargs)
+
+
+@nox.session(python=DEFAULT_PYTHON_VERSION)
+def cover(session):
+    """Run the final coverage report.
+
+    This outputs the coverage report aggregating coverage from the unit
+    test runs (not system test runs), and then erases coverage data.
+    """
+    session.install("coverage", "pytest-cov")
+    session.run("coverage", "report", "--show-missing", "--fail-under=100")
+    session.run("coverage", "erase")
 
 
 @nox.session(python="3.10")

packages/google-crc32c/src/google_crc32c/__init__.py

@@ -20,11 +20,12 @@
     "please configure a c build environment and compile the extension"
 )
 
-# Default to C exstension Implementation, falling back to pure python.
+# Default to C extension implementation, falling back to pure Python.
 try:
-    from google_crc32c import cext as impl
+    # Pure-Python unit test sessions test python.py; cext is tested during wheel checks.
+    from google_crc32c import cext as impl  # pragma: NO COVER
 
-    implementation = "c"
+    implementation = "c"  # pragma: NO COVER
 except ImportError:
     from google_crc32c import python as impl  # type: ignore
 

packages/google-crc32c/src/google_crc32c/cext.py

@@ -17,8 +17,8 @@
 import google_crc32c.__config__  # noqa: F401
 from google_crc32c._checksum import CommonChecksum
 from google_crc32c._crc32c import (  # type: ignore
-    extend,  # type: ignore
-    value,  # type: ignore
+    extend,
+    value,
 )
 
 

packages/google-crc32c/tests/test___init__.py

@@ -206,10 +206,13 @@ def _crc32c(request):
 
         return python
     elif request.param == "cext":
-        from google_crc32c import cext
+        try:
+            from google_crc32c import cext
 
-        return cext
-    else:
+            return cext  # pragma: NO COVER
+        except ImportError:  # pragma: NO COVER
+            pytest.skip("C extension not compiled")  # pragma: NO COVER
+    else:  # pragma: NO COVER
         raise ValueError("invalid internal test config")
 
 
@@ -225,6 +228,17 @@ def test_ctor_explicit(_crc32c):
         helper = google_crc32c.Checksum(chunk)
         assert helper._crc == google_crc32c.value(chunk)
 
+    @staticmethod
+    def test_update_array():
+        import array
+
+        from google_crc32c import python
+
+        chunk = array.array("B", b"DEADBEEF")
+        helper = python.Checksum()
+        helper.update(chunk)
+        assert helper._crc == python.value(b"DEADBEEF")
+
     @staticmethod
     def test_update(_crc32c):
         chunk = b"DEADBEEF"
@@ -287,3 +301,18 @@ def test_consume_stream(_crc32c, chunksize):
         assert found == expected
         for call in stream.read.call_args_list:
             assert call == mock.call(chunksize)
+
+
+def test_common_checksum():
+    from google_crc32c._checksum import CommonChecksum
+
+    class DummyChecksum(CommonChecksum):
+        __slots__ = ("_crc",)
+
+    checksum = DummyChecksum()
+    assert checksum._crc == 0
+    with pytest.raises(NotImplementedError):
+        checksum.update(b"data")
+
+    with pytest.raises(NotImplementedError):
+        DummyChecksum(b"foo")