Handle libmagic versions that don't support MAGIC_EXTENSION

extension support was added to libmagic in 2015 in
9190a18d09f25fb0ca6abe1fcbdba780f5077e45.  This change:

 - updates the test to handle various verions that return garbage /
   empty string.s
- throws an exception in magic.Magic if extension support is requested
  and we know its not supported.

2 files changed, 14 insertions, 5 deletions

diff --git a/magic.py b/magic.py
index 773e4ae..aab7987 100644
--- a/magic.py
+++ b/magic.py
@@ -70,6 +70,10 @@ class Magic:
 
         magic_load(self.cookie, magic_file)
 
+        # MAGIC_EXTENSION was added in 523 or 524, so bail if
+        # it doesn't appear to be available
+        if extension and (not _has_version or version() < 524):
+            raise NotImplementedError('MAGIC_EXTENSION is not supported in this version of libmagic')
 
         # For https://github.com/ahupp/python-magic/issues/190
         # libmagic has fixed internal limits that some files exceed, causing
diff --git a/test/test.py b/test/test.py
index 15a4115..eb5af89 100755
--- a/test/test.py
+++ b/test/test.py
@@ -112,11 +112,16 @@ class MagicTest(unittest.TestCase):
             del os.environ['TZ']
 
     def test_extension(self):
-        m = magic.Magic(extension=True)
-        self.assert_values(m, {
-            'test.gz': 'gz/tgz/tpz/zabw/svgz',
-            'name_use.jpg': 'jpeg/jpg/jpe/jfif',
-        })
+        try:
+            m = magic.Magic(extension=True)
+            self.assert_values(m, {
+                # some versions return '' for the extensions of a gz file,
+                # including w/ the command line.  Who knows...
+                'test.gz': ('gz/tgz/tpz/zabw/svgz', '', '???'),
+                'name_use.jpg': 'jpeg/jpg/jpe/jfif',
+            })
+        except NotImplementedError:
+            self.skipTest('MAGIC_EXTENSION not supported in this version')
 
     def test_unicode_result_nonraw(self):
         m = magic.Magic(raw=False)