[primer] Add multi_package test fixture

Test comparator output across two packages with different change
categories: astroid has a changed diagnostic, astropy has a new
false positive and a removed message.

Author: Pierre-Sassoulas

tests/testutils/_primer/cases/multi_package/expected.txt

@@ -0,0 +1,45 @@
+🤖 **Effect of this PR on checked open source code:** 🤖
+
+
+**Effect on [astroid](https://github.com/pylint-dev/astroid):**
+
+The following messages are now emitted:
+
+<details>
+
+1) too-complex:
+*'my_function' is too complex. The McCabe rating is 17*
+https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L105
+</details>
+
+The following messages are no longer emitted:
+
+<details>
+
+1) too-complex:
+*'my_function' is too complex. The McCabe rating is 18*
+https://github.com/pylint-dev/astroid/blob/123456789abcdef/astroid/node_classes.py#L100
+</details>
+
+
+**Effect on [astropy](https://github.com/astropy/astropy):**
+
+The following messages are now emitted:
+
+<details>
+
+1) locally-disabled:
+*Locally disabling looping-through-iterator (W4801)*
+https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
+</details>
+
+The following messages are no longer emitted:
+
+<details>
+
+1) useless-suppression:
+*Useless suppression of 'looping-through-iterator'*
+https://github.com/astropy/astropy/blob/1fb40bc1f22f176254ef583065aa155f53f3b414/astropy/coordinates/angles/angle_parsetab.py#L14
+</details>
+
+*This comment was generated for commit v2.14.2*

tests/testutils/_primer/cases/multi_package/expected_comparator.json

@@ -0,0 +1,4 @@
+[
+  { "package": "astroid", "missing": 1, "new": 1 },
+  { "package": "astropy", "missing": 1, "new": 1 }
+]

tests/testutils/_primer/cases/multi_package/main.json

@@ -0,0 +1,42 @@
+{
+  "astroid": {
+    "commit": "1234567890abcdef",
+    "messages": [
+      {
+        "type": "convention",
+        "module": "astroid.node_classes",
+        "obj": "my_function",
+        "line": 100,
+        "column": 0,
+        "endLine": 100,
+        "endColumn": 15,
+        "path": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/node_classes.py",
+        "symbol": "too-complex",
+        "message": "'my_function' is too complex. The McCabe rating is 18",
+        "messageId": "R1260",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/node_classes.py"
+      }
+    ]
+  },
+  "astropy": {
+    "commit": "1fb40bc1f22f176254ef583065aa155f53f3b414",
+    "messages": [
+      {
+        "type": "warning",
+        "module": "astropy.coordinates.angles.angle_parsetab",
+        "obj": "",
+        "line": 14,
+        "column": 0,
+        "endLine": null,
+        "endColumn": null,
+        "path": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py",
+        "symbol": "useless-suppression",
+        "message": "Useless suppression of 'looping-through-iterator'",
+        "messageId": "I0021",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py"
+      }
+    ]
+  }
+}

tests/testutils/_primer/cases/multi_package/pr.json

@@ -0,0 +1,42 @@
+{
+  "astroid": {
+    "commit": "123456789abcdef",
+    "messages": [
+      {
+        "type": "convention",
+        "module": "astroid.node_classes",
+        "obj": "my_function",
+        "line": 105,
+        "column": 0,
+        "endLine": 105,
+        "endColumn": 15,
+        "path": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/node_classes.py",
+        "symbol": "too-complex",
+        "message": "'my_function' is too complex. The McCabe rating is 17",
+        "messageId": "R1260",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/pylint-dev/astroid/astroid/node_classes.py"
+      }
+    ]
+  },
+  "astropy": {
+    "commit": "1fb40bc1f22f176254ef583065aa155f53f3b414",
+    "messages": [
+      {
+        "type": "info",
+        "module": "astropy.coordinates.angles.angle_parsetab",
+        "obj": "",
+        "line": 14,
+        "column": 0,
+        "endLine": null,
+        "endColumn": null,
+        "path": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py",
+        "symbol": "locally-disabled",
+        "message": "Locally disabling looping-through-iterator (W4801)",
+        "messageId": "I0011",
+        "confidence": "UNDEFINED",
+        "absolutePath": "tests/.pylint_primer_tests/astropy/astropy/astropy/coordinates/angles/angle_parsetab.py"
+      }
+    ]
+  }
+}