ghostscript: improve test coverage of error cases

src/ocrmypdf/_exec/ghostscript.py

@@ -71,7 +71,8 @@ def jpeg_passthrough_available() -> bool:
 
 
 def _gs_error_reported(stream) -> bool:
-    return True if re.search(r'error', stream, flags=re.IGNORECASE) else False
+    match = re.search(r'error', stream, flags=re.IGNORECASE)
+    return bool(match)
 
 
 def rasterize_pdf(
@@ -160,16 +161,14 @@ class GhostscriptFollower:
         if not self.progressbar_class:
             return
         if not self.progressbar:
-            m = self.re_process.match(line.strip())
-            if m:
+            if m := self.re_process.match(line.strip()):
                 self.count = int(m.group(1))
                 self.progressbar = self.progressbar_class(
                     total=self.count, desc="PDF/A conversion", unit='page'
                 )
                 return
         else:
-            m = self.re_page.match(line.strip())
-            if m:
+            if self.re_page.match(line.strip()):
                 self.progressbar.update()
 
 

tests/test_ghostscript.py

@@ -6,11 +6,13 @@
 
 
 import logging
+import subprocess
 from decimal import Decimal
+from unittest.mock import patch
 
 import pikepdf
 import pytest
-from PIL import Image
+from PIL import Image, UnidentifiedImageError
 
 from ocrmypdf._exec.ghostscript import rasterize_pdf
 from ocrmypdf.exceptions import ExitCode
@@ -124,3 +126,20 @@ def test_ghostscript_feature_elision(resources, outpdf):
         '--plugin',
         'tests/plugins/gs_feature_elision.py',
     )
+
+
+def test_rasterize_pdf_errors(resources, no_outpdf, caplog):
+    with patch('ocrmypdf._exec.ghostscript.run') as mock:
+        # ghostscript can produce
+        mock.return_value = subprocess.CompletedProcess(
+            ['fakegs'], returncode=0, stdout=b'', stderr=b'error this is an error'
+        )
+        with pytest.raises(UnidentifiedImageError):
+            rasterize_pdf(
+                resources / 'francais.pdf',
+                no_outpdf,
+                raster_device='pngmono',
+                raster_dpi=Resolution(100, 100),
+            )
+        assert "this is an error" in caplog.text
+        assert "invalid page image file" in caplog.text