Fix version checker failing for qpdf 10.0.0

Fixes #527

src/ocrmypdf/exec/__init__.py

@@ -23,6 +23,7 @@ import re
 import shutil
 import sys
 from collections.abc import Mapping
+from distutils.version import LooseVersion
 from functools import lru_cache
 from subprocess import PIPE, STDOUT, CalledProcessError
 from subprocess import run as subprocess_run
@@ -270,7 +271,7 @@ def check_external_program(
             raise MissingDependencyError()
         return
 
-    if found_version < need_version:
+    if LooseVersion(found_version) < LooseVersion(need_version):
         _error_old_version(program, package, need_version, found_version, required_for)
         if not recommended:
             raise MissingDependencyError()

tests/test_validation.py

@@ -176,3 +176,31 @@ def test_language_warning(caplog):
         vd.check_options_languages(opts)
         assert opts.language == ['eng']
         assert 'assuming --language' in caplog.text
+
+
+def test_version_comparison():
+    vd.check_external_program(
+        program="dummy_basic",
+        package="dummy",
+        version_checker=lambda: '9.0',
+        need_version='8.0.2',
+    )
+    vd.check_external_program(
+        program="dummy_doubledigit",
+        package="dummy",
+        version_checker=lambda: '10.0',
+        need_version='8.0.2',
+    )
+    vd.check_external_program(
+        program="tesseract",
+        package="tesseract",
+        version_checker=lambda: '4.0.0-beta.1',
+        need_version='4.0.0',
+    )
+    with pytest.raises(MissingDependencyError):
+        vd.check_external_program(
+            program="dummy_fails",
+            package="dummy",
+            version_checker=lambda: '1.0',
+            need_version='2.0',
+        )