test add api test=develop

doc/fluid/api/nn.rst

@@ -49,6 +49,7 @@ paddle.nn
     nn/exponential_decay.rst
     nn/filter_by_instag.rst
     nn/fsp_matrix.rst
+    nn/functional.rst
     nn/gather_tree.rst
     nn/gelu.rst
     nn/generate_mask_labels.rst

doc/fluid/api/nn/functional.rst

+=========
+functional
+=========
+
+..  toctree::
+    :maxdepth: 1
+
+    functional/l1_loss.rst

doc/fluid/api/nn/functional/l1_loss.rst

+.. _api_nn_functional_l1_loss:
+
+l1_loss
+------
+
+..  autoclass:: paddle.nn.functional.l1_loss
+    :members:
+    :inherited-members:
+    :noindex: