Test that our CFF2CharStringMergePen source order fix is effective

tests/test_workflow.py

@@ -1,15 +1,31 @@
+from __future__ import annotations
+
 import pathlib
+import random
 import subprocess
+from dataclasses import dataclass, replace
 
 import pytest
 import yaml
+from fontra.core.classes import VariableGlyph
+from fontra.workflow.actions import registerFilterAction
+from fontra.workflow.actions.base import BaseFilter
 from fontra.workflow.workflow import Workflow
 from test_compile import cleanupTTX
 
 testDir = pathlib.Path(__file__).resolve().parent
 dataDir = testDir / "data"
 
 
+@registerFilterAction("randomize-glyph-source-order")
+@dataclass(kw_only=True)
+class RandomizeGlyphSourceOrder(BaseFilter):
+    async def processGlyph(self, glyph: VariableGlyph) -> VariableGlyph:
+        newSources = list(glyph.sources)
+        random.shuffle(newSources)
+        return replace(glyph, sources=newSources)
+
+
 testData = [
     (
         """
@@ -33,6 +49,20 @@
     ),
     (
         """
+# This test confirms that the order of sources in glyphs is irrelevant.
+# In other words, check that we produce the same output regardless of glyph
+# source order.
+steps:
+- input: fontra-read
+  source: "tests/data/MutatorSans.fontra"
+- filter: randomize-glyph-source-order
+- output: compile-varc
+  destination: "output-random-source-order.otf"
+""",
+        "MutatorSans.otf.ttx",
+    ),
+    (
+        """
 steps:
 - input: fontra-read
   source: "tests/data/MutatorSans.fontra"