[primer] refactor the test to use a common function

tests/testutils/_primer/test_primer.py

@@ -3,6 +3,8 @@
 # Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt
 
 """Test the primer commands. """
+from __future__ import annotations
+
 import sys
 from pathlib import Path
 from unittest.mock import patch
@@ -46,35 +48,44 @@ class TestPrimer:
         ],
     )
     def test_compare(self, directory: Path) -> None:
-        main = directory / "main.json"
-        pr = directory / "pr.json"
-        expected_file = directory / "expected.txt"
-        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:
-            content = f.read()
-        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")
+        """Test for the standard case.
+
+        Directory in 'fixtures/' with 'main.json', 'pr.json' and 'expected.txt'."""
+        self.__assert_expected(directory)
 
     def test_truncated_compare(self) -> 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"
+        """Test for the truncation of comment that are too long."""
+        max_comment_length = 500
+        directory = FIXTURES_PATH / "message_changed"
+        with patch(
+            "pylint.testutils._primer.primer_compare_command.MAX_GITHUB_COMMENT_LENGTH",
+            max_comment_length,
+        ):
+            content = self.__assert_expected(
+                directory, expected_file=directory / "expected_truncated.txt"
+            )
+        assert len(content) < max_comment_length
+
+    @staticmethod
+    def __assert_expected(
+        directory: Path,
+        main: Path | None = None,
+        pr: Path | None = None,
+        expected_file: Path | None = None,
+    ) -> str:
+        if main is None:
+            main = directory / "main.json"
+        if pr is None:
+            pr = directory / "pr.json"
+        if expected_file is None:
+            expected_file = directory / "expected.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()
+            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")
+        return content