diff --git a/beets/test/_common.py b/beets/test/_common.py
index 7c7defb02..0d2d51f1e 100644
--- a/beets/test/_common.py
+++ b/beets/test/_common.py
@@ -115,11 +115,6 @@ def import_session(lib=None, loghandler=None, paths=[], query=[], cli=False):
 class Assertions:
     """A mixin with additional unit test assertions."""
 
-    def assertIsFile(self, path):
-        path = Path(os.fsdecode(path))
-        assert path.exists()
-        assert path.is_file()
-
     def assertIsDir(self, path):
         path = Path(os.fsdecode(path))
         assert path.exists()
diff --git a/test/plugins/test_convert.py b/test/plugins/test_convert.py
index e889ce7bb..25a000284 100644
--- a/test/plugins/test_convert.py
+++ b/test/plugins/test_convert.py
@@ -58,13 +58,18 @@ class ConvertMixin:
             shell_quote(sys.executable), shell_quote(stub), tag
         )
 
+    def assert_is_file(self, path):
+        path = Path(os.fsdecode(path))
+        assert path.exists()
+        assert path.is_file()
+
     def assertFileTag(self, path, tag):
         """Assert that the path is a file and the files content ends
         with `tag`.
         """
         display_tag = tag
         tag = tag.encode("utf-8")
-        self.assertIsFile(path)
+        self.assert_is_file(path)
         with open(path, "rb") as f:
             f.seek(-len(display_tag), os.SEEK_END)
             assert f.read() == tag, (
@@ -77,7 +82,7 @@ class ConvertMixin:
         """
         display_tag = tag
         tag = tag.encode("utf-8")
-        self.assertIsFile(path)
+        self.assert_is_file(path)
         with open(path, "rb") as f:
             f.seek(-len(tag), os.SEEK_END)
             assert f.read() != tag, (
@@ -117,7 +122,7 @@ class ImportConvertTest(AsIsImporterMixin, ImportHelper, ConvertTestCase):
 
         item = self.lib.items().get()
         assert item is not None
-        self.assertIsFile(item.path)
+        self.assert_is_file(item.path)
 
     def test_delete_originals(self):
         self.config["convert"]["delete_originals"] = True