diff --git a/tensorflow_datasets/core/download/download_manager.py b/tensorflow_datasets/core/download/download_manager.py
index 4dcd9fc0439..958476a7e3a 100644
--- a/tensorflow_datasets/core/download/download_manager.py
+++ b/tensorflow_datasets/core/download/download_manager.py
@@ -368,4 +368,5 @@ def _wait_on_promise(p):
 def _map_promise(map_fn, all_inputs):
   """Map the function into each element and resolve the promise."""
   all_promises = utils.map_nested(map_fn, all_inputs)  # Apply the function
-  return utils.map_nested(_wait_on_promise, all_promises)
+  res = utils.map_nested(_wait_on_promise, all_promises)
+  return res
diff --git a/tensorflow_datasets/core/download/download_manager_test.py b/tensorflow_datasets/core/download/download_manager_test.py
index f30476fa3c0..7a717ead0b2 100644
--- a/tensorflow_datasets/core/download/download_manager_test.py
+++ b/tensorflow_datasets/core/download/download_manager_test.py
@@ -28,6 +28,7 @@
 
 import promise
 import tensorflow as tf
+from tensorflow_datasets.core import utils
 from tensorflow_datasets.core.download import download_manager as dm
 from tensorflow_datasets.core.download import resource as resource_lib
 
@@ -150,11 +151,12 @@ def test_download(self):
     downloaded_b.set()
     downloaded_c.set()
     downloads = manager.download(urls)
-    self.assertEqual(downloads, {
+    expected = {
         'cached': '/dl_dir/%s' % afname,
         'new': '/dl_dir/%s' % bfname,
         'info_deleted': '/dl_dir/%s' % cfname,
-    })
+    }
+    self.assertEqual(downloads, expected)
 
   def test_extract(self):
     """One file already extracted, one file with NO_EXTRACT, one to extract."""
@@ -174,11 +176,12 @@ def test_extract(self):
     manager = self._get_manager()
     extracted_new.set()
     res = manager.extract(files)
-    self.assertEqual(res, {
+    expected = {
         'cached': '/extract_dir/ZIP.%s' % resource_cached.fname,
         'new': '/extract_dir/TAR.%s' % resource_new.fname,
         'noextract': '/dl_dir/%s' % resource_noextract.fname,
-    })
+    }
+    self.assertEqual(res, expected)
 
   def test_extract_twice_parallel(self):
     # Make sure calling extract twice on same resource actually does the
@@ -189,9 +192,11 @@ def test_extract_twice_parallel(self):
     extracted_new.set()
     out1 = manager.extract(['/dl_dir/foo.tar', '/dl_dir/foo.tar'])
     out2 = manager.extract('/dl_dir/foo.tar')
-    self.assertEqual(out1[0], '/extract_dir/TAR.foo')
-    self.assertEqual(out1[1], '/extract_dir/TAR.foo')
-    self.assertEqual(out2, '/extract_dir/TAR.foo')
+    expected = '/extract_dir/TAR.foo'
+    self.assertEqual(out1[0], expected)
+    self.assertEqual(out1[1], expected)
+    expected = '/extract_dir/TAR.foo'
+    self.assertEqual(out2, expected)
     # Result is memoize so extract has only been called once
     self.assertEqual(1, self.extractor_extract.call_count)
 
@@ -216,9 +221,11 @@ def test_download_and_extract(self):
     manager._checksums[url_a] = sha_contenta
     manager._checksums[url_b] = sha_contentb
     res = manager.download_and_extract({'a': url_a, 'b': url_b})
-    self.assertEqual(res, {
+    expected = {
         'a': '/extract_dir/ZIP.%s' % resource_a.fname,
-        'b': '/dl_dir/%s' % resource_b.fname})
+        'b': '/dl_dir/%s' % resource_b.fname,
+    }
+    self.assertEqual(res, expected)
 
   def test_download_and_extract_already_downloaded(self):
     url_a = 'http://a/a.zip'
@@ -233,7 +240,8 @@ def test_download_and_extract_already_downloaded(self):
     ext_a.set()
     manager = self._get_manager()
     res = manager.download_and_extract(url_a)
-    self.assertEqual(res, '/extract_dir/ZIP.%s' % resource_a.fname)
+    expected = '/extract_dir/ZIP.%s' % resource_a.fname
+    self.assertEqual(res, expected)
 
   def test_force_download_and_extract(self):
     url = 'http://a/b.tar.gz'
@@ -253,7 +261,8 @@ def test_force_download_and_extract(self):
     manager = self._get_manager(force_download=True, force_extraction=True,
                                 checksums={url: resource_.sha256})
     res = manager.download_and_extract(url)
-    self.assertEqual('/extract_dir/TAR_GZ.%s' % resource_.fname, res)
+    expected = '/extract_dir/TAR_GZ.%s' % resource_.fname
+    self.assertEqual(expected, res)
     # Rename after download:
     (from_, to), kwargs = self.gfile.rename.call_args
     self.assertTrue(re.match(