Give the test document a filename

wagtail/tests/testapp/fixtures/test.json

@@ -616,7 +616,8 @@
     "model": "wagtaildocs.Document",
     "fields": {
         "title": "test document",
-        "created_at": "2014-01-01T12:00:00.000Z"
+        "created_at": "2014-01-01T12:00:00.000Z",
+        "file": "documents/test.pdf"
     }
 },
 {

wagtail/wagtaildocs/tests.py

@@ -679,7 +679,7 @@ class TestDocumentRichTextLinkHandler(TestCase):
             True
         )
         self.assertEqual(result,
-                         '<a data-linktype="document" data-id="1" href="/documents/1/">')
+                         '<a data-linktype="document" data-id="1" href="/documents/1/test.pdf">')
 
     def test_expand_db_attributes_not_for_editor(self):
         result = DocumentLinkHandler.expand_db_attributes(
@@ -687,4 +687,4 @@ class TestDocumentRichTextLinkHandler(TestCase):
             False
         )
         self.assertEqual(result,
-                         '<a href="/documents/1/">')
+                         '<a href="/documents/1/test.pdf">')