tests: account for test that expected pngquant for windows

tests/test_pdfa.py

@@ -4,23 +4,31 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+import os
+
 import pikepdf
 import pytest
 
+from ocrmypdf.exceptions import MissingDependencyError
+
 from .conftest import check_ocrmypdf
 
 
 @pytest.mark.parametrize('optimize', (0, 3))
 @pytest.mark.parametrize('pdfa_level', (1, 2, 3))
 def test_pdfa(resources, outpdf, optimize, pdfa_level):
-    check_ocrmypdf(
-        resources / 'francais.pdf',
-        outpdf,
-        '--plugin',
-        'tests/plugins/tesseract_noop.py',
-        f'--output-type=pdfa-{pdfa_level}',
-        f'--optimize={optimize}',
-    )
+    try:
+        check_ocrmypdf(
+            resources / 'francais.pdf',
+            outpdf,
+            '--plugin',
+            'tests/plugins/tesseract_noop.py',
+            f'--output-type=pdfa-{pdfa_level}',
+            f'--optimize={optimize}',
+        )
+    except MissingDependencyError as e:
+        if 'pngquant' in str(e) and optimize in (2, 3) and os.name == 'nt':
+            pytest.xfail("pngquant currently not available on Windows")
     if pdfa_level in (2, 3):
         # PDF/A-2 allows ObjStm
         assert b'/ObjStm' in outpdf.read_bytes()