[tests][dask] simplify fit calls in Dask tests (#4018)

* simplify fit calls in Dask tests

* Update .vsts-ci.yml

* Update .vsts-ci.yml

tests/python_package_test/test_dask.py

@@ -1046,10 +1046,7 @@ def test_network_params_not_required_but_respected_if_given(client, task, output
         n_estimators=5,
         num_leaves=5,
     )
-    if task == 'ranking':
-        dask_model1.fit(dX, dy, group=dg)
-    else:
-        dask_model1.fit(dX, dy)
+    dask_model1.fit(dX, dy, group=dg)
     assert dask_model1.fitted_
     params = dask_model1.get_params()
     assert 'local_listen_port' not in params
@@ -1067,10 +1064,7 @@ def test_network_params_not_required_but_respected_if_given(client, task, output
         ]),
     )
 
-    if task == 'ranking':
-        dask_model2.fit(dX, dy, group=dg)
-    else:
-        dask_model2.fit(dX, dy)
+    dask_model2.fit(dX, dy, group=dg)
     assert dask_model2.fitted_
     params = dask_model2.get_params()
     assert 'local_listen_port' not in params
@@ -1086,10 +1080,7 @@ def test_network_params_not_required_but_respected_if_given(client, task, output
     )
     error_msg = "has multiple Dask worker processes running on it"
     with pytest.raises(lgb.basic.LightGBMError, match=error_msg):
-        if task == 'ranking':
-            dask_model3.fit(dX, dy, group=dg)
-        else:
-            dask_model3.fit(dX, dy)
+        dask_model3.fit(dX, dy, group=dg)
 
     client.close(timeout=CLIENT_CLOSE_TIMEOUT)
 
@@ -1141,10 +1132,7 @@ def test_machines_should_be_used_if_provided(task, output):
         with pytest.raises(lgb.basic.LightGBMError, match=error_msg):
             with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
                 s.bind(('127.0.0.1', open_ports[0]))
-                if task == 'ranking':
-                    dask_model.fit(dX, dy, group=dg)
-                else:
-                    dask_model.fit(dX, dy)
+                dask_model.fit(dX, dy, group=dg)
 
 
 @pytest.mark.parametrize(
@@ -1232,6 +1220,7 @@ def test_training_succeeds_when_data_is_dataframe_and_label_is_column_array(
     model = model_factory(**params)
     model.fit(dX, dy_col_array, sample_weight=dw, group=dg)
     assert model.fitted_
+
     client.close(timeout=CLIENT_CLOSE_TIMEOUT)