syntax highlighting on changed lines, keeping the red/green background

tests/conftest.py

@@ -1,7 +1,25 @@
 import os
 import sys
 
+import pytest
+
 # tests import the package directly; sublime/sublime_plugin come from tests/stubs
 HERE = os.path.dirname(os.path.abspath(__file__))
 sys.path.insert(0, os.path.dirname(HERE))
 sys.path.insert(0, os.path.join(HERE, "stubs"))
+
+
+@pytest.fixture(autouse=True)
+def scheme_override_sandbox(tmp_path, monkeypatch):
+    """Keep the colour-scheme override palette.py writes inside the test's own tmp_path
+
+    Both caches are per session and the stub hands every view the same id, so they would otherwise
+    leak between tests and make every assertion about the override depend on test order.
+    """
+    import sublime
+
+    from vdiff import palette, state
+
+    palette.reset()
+    monkeypatch.setattr(state, "STATES", {})
+    monkeypatch.setattr(sublime, "packages_path", lambda: str(tmp_path))