[primer] Add a test for truncating comments

Author: Pierre-Sassoulas

tests/testutils/_primer/fixtures/message_changed/expected_truncated.txt

@@ -0,0 +1,20 @@
+🤖 **Effect of this PR on checked open source code:** 🤖
+
+
+
+**Effect on [astroid](https://github.com/PyCQA/astroid):**
+The following messages are now emitted:
+
+<details>
+
+1) locally-disabled:
+*Locally disabling redefined-builtin [we added some text in the message] (W0622)*
+https://github.com/PyCQA/astroid/blob/main/astroid/__init__.py#L91
+
+</details>
+
+The fol...
+
+*This comment was truncated because GitHub allows only 500 characters in a comment.*
+
+*This comment was generated for commit v2.14.2*

tests/testutils/_primer/test_primer.py

@@ -20,15 +20,21 @@
 
 PRIMER_CURRENT_INTERPRETER = (3, 10)
 
-
-@pytest.mark.skipif(
-    sys.platform in {"win32", "darwin"},
-    reason="Primers are internal will never be run on costly github action (mac or windows)",
+OS_SKIP_REASON = (
+    "Primers are internal will never be run on costly github action (mac or windows)"
 )
-@pytest.mark.skipif(
-    sys.version_info[:2] != PRIMER_CURRENT_INTERPRETER or IS_PYPY,
-    reason=f"Primers are internal will always be run for only one interpreter (currently {PRIMER_CURRENT_INTERPRETER})",
+INTERPRETER_SKIP_REASON = (
+    "Primers are internal will always be run for only one interpreter (currently"
+    f" {PRIMER_CURRENT_INTERPRETER})"
 )
+
+NOT_PRIMER_OS = sys.platform in {"win32", "darwin"}
+NOT_PRIMER_INTERPRETER = sys.version_info[:2] != PRIMER_CURRENT_INTERPRETER or IS_PYPY
+DEFAULT_ARGS = ["python tests/primer/__main__.py", "compare", "--commit=v2.14.2"]
+
+
+@pytest.mark.skipif(NOT_PRIMER_OS, reason=OS_SKIP_REASON)
+@pytest.mark.skipif(NOT_PRIMER_INTERPRETER, reason=INTERPRETER_SKIP_REASON)
 @pytest.mark.parametrize(
     "directory",
     [
@@ -41,13 +47,7 @@ def test_compare(directory: Path) -> None:
     main = directory / "main.json"
     pr = directory / "pr.json"
     expected_file = directory / "expected.txt"
-    new_argv = [
-        "python tests/primer/__main__.py",
-        "compare",
-        "--commit=v2.14.2",
-        f"--base-file={main}",
-        f"--new-file={pr}",
-    ]
+    new_argv = DEFAULT_ARGS + [f"--base-file={main}", f"--new-file={pr}"]
     with patch("sys.argv", new_argv):
         Primer(PRIMER_DIRECTORY, PACKAGES_TO_PRIME_PATH).run()
     with open(PRIMER_DIRECTORY / "comment.txt", encoding="utf8") as f:
@@ -56,3 +56,26 @@ def test_compare(directory: Path) -> None:
         expected = f.read()
     # rstrip so the expected.txt can end with a newline
     assert content == expected.rstrip("\n")
+
+
+@pytest.mark.skipif(NOT_PRIMER_OS, reason=OS_SKIP_REASON)
+@pytest.mark.skipif(NOT_PRIMER_INTERPRETER, reason=INTERPRETER_SKIP_REASON)
+def test_truncated_compare() -> None:
+    FAKE_MAX_GITHUB_COMMENT_LENGTH = 500
+    main = FIXTURES_PATH / "message_changed/main.json"
+    pr = FIXTURES_PATH / "message_changed/pr.json"
+    expected_file = FIXTURES_PATH / "message_changed/expected_truncated.txt"
+    new_argv = DEFAULT_ARGS + [f"--base-file={main}", f"--new-file={pr}"]
+    with patch("sys.argv", new_argv):
+        with patch(
+            "pylint.testutils._primer.primer_compare_command.MAX_GITHUB_COMMENT_LENGTH",
+            FAKE_MAX_GITHUB_COMMENT_LENGTH,
+        ):
+            Primer(PRIMER_DIRECTORY, PACKAGES_TO_PRIME_PATH).run()
+    with open(PRIMER_DIRECTORY / "comment.txt", encoding="utf8") as f:
+        content = f.read()
+    assert len(content) < FAKE_MAX_GITHUB_COMMENT_LENGTH
+    with open(expected_file, encoding="utf8") as f:
+        expected = f.read()
+    # rstrip so the expected.txt can end with a newline
+    assert content == expected.rstrip("\n")