test compression twice to ensure we test the stat path

tests/test_compress_assets_plugin.py

@@ -39,12 +39,23 @@ def test_compress(disconnect_signals, settings, tmpdir, method,
                   compress_suffix, test_import):
     if test_import:
         pytest.importorskip(test_import)
-    compress_options = make_gallery(settings, tmpdir, method)
 
-    suffixes = compress_options['suffixes']
+    # Compress twice to test compression skip based on mtime
+    for _ in range(2):
+        compress_options = make_gallery(settings, tmpdir, method)
+
+        suffixes = compress_options['suffixes']
+
+        for path, dirs, files in os.walk(settings['destination']):
+            for file in files:
+                original_filename = os.path.join(path, file)
+                compressed_filename = '{}.{}'.format(os.path.join(path, file), compress_suffix)
+                path_exists = os.path.exists(compressed_filename)
+                file_ext = os.path.splitext(file)[1][1:]
+                if file_ext in suffixes:
+                    assert path_exists
+                    assert os.stat(original_filename).st_mtime <= os.stat(compressed_filename).st_mtime
+                else:
+                    assert not path_exists
+                assert path_exists if file_ext in suffixes else not path_exists
 
-    for path, dirs, files in os.walk(settings['destination']):
-        for file in files:
-            path_exists = os.path.exists('{}.{}'.format(os.path.join(path, file), compress_suffix))
-            file_ext = os.path.splitext(file)[1][1:]
-            assert path_exists if file_ext in suffixes else not path_exists