test: factor out a tools_missing() function

tests/comparators/test_utils.py

@@ -24,7 +24,7 @@ from diffoscope.config import Config
 from diffoscope.difference import Difference
 from diffoscope.comparators.utils import Command
 
-from utils import skip_unless_tools_exist, data, load_fixture
+from utils import tools_missing, skip_unless_tools_exist, data, load_fixture
 
 try:
     import tlsh # noqa
@@ -36,6 +36,12 @@ fuzzy_tar1 = load_fixture(data('fuzzy1.tar'))
 fuzzy_tar2 = load_fixture(data('fuzzy2.tar'))
 fuzzy_tar3 = load_fixture(data('fuzzy3.tar'))
 
+def test_tools_missing():
+    assert tools_missing() is True
+    assert tools_missing('/missing') is True
+    for x in ['cat', 'sh']:
+        assert tools_missing(x) is False
+
 @skip_unless_tools_exist()
 def test_skip_unless_tools_exist_empty():
     pytest.xfail("Test should always be skipped")

tests/comparators/utils.py

@@ -36,9 +36,12 @@ from diffoscope.comparators.binary import FilesystemFile, NonExistingFile
 def set_locale():
     diffoscope.set_locale()
 
+def tools_missing(*required):
+    return not required or any(find_executable(x) is None for x in required)
+
 def skip_unless_tools_exist(*required):
     return pytest.mark.skipif(
-        not required or any(find_executable(x) is None for x in required),
+        tools_missing(*required),
         reason="requires {}".format(" and ".join(required)),
     )