add test to make sure that when a bogus hash entry is entered, it gets caught

casimport/__init__.py

@@ -669,3 +669,23 @@ class Test(unittest.TestCase):
 		# a local ipfs gateway makes more sense than hitting a
 		# public gateway
 		pass
+
+	def test_filecorruption(self):
+		cachedir = self.tempdir / 'cachedir'
+		cachedir.mkdir()
+
+		# that an existing file
+		shutil.copy(self.fixtures / 'hello.py', cachedir)
+
+		# is in the cache
+		fdcas = FileDirCAS(cachedir)
+
+		# that when refresh is surpressed
+		fdcas.refresh_dir = lambda: None
+
+		# and has a bogus hash
+		fdcas._hashes['0000'] = cachedir / 'hello.py'
+
+		# that when read raises an exception
+		with self.assertRaises(ValueError):
+			fdcas.fetch_data(urllib.parse.urlparse('hash://sha256/0000'))