Add tests for Comparator class

Test all fixture scenarios (no change, both empty, new/removed/changed
messages, batched) against expected_comparator.json files.
100% coverage on comparator.py.

Author: Pierre-Sassoulas

tests/testutils/_primer/fixtures/batched/expected_comparator.json

@@ -0,0 +1 @@
+[{"package": "astroid", "missing": 2, "new": 0}]

tests/testutils/_primer/fixtures/both_empty/expected_comparator.json

@@ -0,0 +1 @@
+[]

tests/testutils/_primer/fixtures/message_changed/expected_comparator.json

@@ -0,0 +1 @@
+[{"package": "astroid", "missing": 1, "new": 1}]

tests/testutils/_primer/fixtures/new_message/expected_comparator.json

@@ -0,0 +1 @@
+[{"package": "astroid", "missing": 0, "new": 1}]

tests/testutils/_primer/fixtures/no_change/expected_comparator.json

@@ -0,0 +1 @@
+[]

tests/testutils/_primer/fixtures/removed_message/expected_comparator.json

@@ -0,0 +1 @@
+[{"package": "astroid", "missing": 1, "new": 0}]

tests/testutils/_primer/test_comparator.py

@@ -2,6 +2,7 @@
 # For details: https://github.com/pylint-dev/pylint/blob/main/LICENSE
 # Copyright (c) https://github.com/pylint-dev/pylint/blob/main/CONTRIBUTORS.txt
 
+import json
 from pathlib import Path
 
 import pytest
@@ -12,56 +13,36 @@
 
 
 @pytest.mark.parametrize(
-    ("fixture", "main_file", "pr_file", "batches", "expected_packages", "expected_missing", "expected_new"),
+    "directory",
     [
-        pytest.param(
-            "both_empty", "main.json", "pr.json", None, [], [], [],
-            id="both_empty",
-        ),
-        pytest.param(
-            "no_change", "main.json", "pr.json", None, [], [], [],
-            id="no_change",
-        ),
-        pytest.param(
-            "new_message", "main.json", "pr.json", None,
-            ["astroid"], [0], [1],
-            id="new_message",
-        ),
-        pytest.param(
-            "removed_message", "main.json", "pr.json", None,
-            ["astroid"], [1], [0],
-            id="removed_message",
-        ),
-        pytest.param(
-            "message_changed", "main.json", "pr.json", None,
-            ["astroid"], [1], [1],
-            id="message_changed",
-        ),
-        pytest.param(
-            "batched", "main_BATCHIDX.json", "pr_BATCHIDX.json", 2,
-            ["astroid"], [2], [0],
-            id="batched",
-        ),
+        pytest.param(p, id=p.name)
+        for p in FIXTURES_PATH.iterdir()
+        if p.is_dir() and p.name != "batched"  # tested separately
     ],
 )
-def test_comparator(
-    fixture: str,
-    main_file: str,
-    pr_file: str,
-    batches: int | None,
-    expected_packages: list[str],
-    expected_missing: list[int],
-    expected_new: list[int],
-) -> None:
-    directory = FIXTURES_PATH / fixture
-    comparator = Comparator(str(directory / main_file), str(directory / pr_file), batches)
+def test_comparator(directory: Path) -> None:
+    """Test Comparator with each fixture directory."""
+    comparator = Comparator(str(directory / "main.json"), str(directory / "pr.json"))
+    expected = json.loads((directory / "expected_comparator.json").read_text("utf-8"))
     results = list(comparator)
-    assert len(results) == len(expected_packages)
-    for (package, missing, new), exp_pkg, exp_miss, exp_new in zip(
-        results, expected_packages, expected_missing, expected_new
-    ):
-        assert package == exp_pkg
-        assert len(missing["messages"]) == exp_miss
-        assert len(new["messages"]) == exp_new
-    # Iterating twice yields the same results
-    assert results == list(comparator)
+    assert len(results) == len(expected)
+    for (package, missing, new), exp in zip(results, expected):
+        assert package == exp["package"]
+        assert len(missing["messages"]) == exp["missing"]
+        assert len(new["messages"]) == exp["new"]
+
+
+def test_comparator_batched() -> None:
+    fixture = FIXTURES_PATH / "batched"
+    comparator = Comparator(
+        str(fixture / "main_BATCHIDX.json"),
+        str(fixture / "pr_BATCHIDX.json"),
+        batches=2,
+    )
+    expected = json.loads((fixture / "expected_comparator.json").read_text("utf-8"))
+    results = list(comparator)
+    assert len(results) == len(expected)
+    for (package, missing, new), exp in zip(results, expected):
+        assert package == exp["package"]
+        assert len(missing["messages"]) == exp["missing"]
+        assert len(new["messages"]) == exp["new"]