Merge pull request matplotlib#22791 from anntzer/ce

TST: Tweak _ConverterError reporting in testing

Author: tacaswell

lib/matplotlib/testing/compare.py

@@ -92,7 +92,7 @@ def _read_until(self, terminator):
         while True:
             c = self._proc.stdout.read(1)
             if not c:
-                raise _ConverterError
+                raise _ConverterError(os.fsdecode(bytes(buf)))
             buf.extend(c)
             if buf.endswith(terminator):
                 return bytes(buf)
@@ -109,7 +109,8 @@ def __call__(self, orig, dest):
             try:
                 self._read_until(b"\nGS")
             except _ConverterError as err:
-                raise OSError("Failed to start Ghostscript") from err
+                raise OSError(
+                    "Failed to start Ghostscript:\n\n" + err.args[0]) from None
 
         def encode_and_escape(name):
             return (os.fsencode(name)
@@ -172,8 +173,9 @@ def __call__(self, orig, dest):
             try:
                 self._read_until(terminator)
             except _ConverterError as err:
-                raise OSError("Failed to start Inkscape in interactive "
-                              "mode") from err
+                raise OSError(
+                    "Failed to start Inkscape in interactive mode:\n\n"
+                    + err.args[0]) from err
 
         # Inkscape's shell mode does not support escaping metacharacters in the
         # filename ("\n", and ":;" for inkscape>=1).  Avoid any problems by