Adding a test for passing backend option in plot

Author: jsignell

pandas/tests/plotting/test_backend.py

@@ -9,7 +9,7 @@
 import pandas
 
 dummy_backend = types.ModuleType("pandas_dummy_backend")
-dummy_backend.plot = lambda *args, **kwargs: None
+dummy_backend.plot = lambda *args, **kwargs: 'used_dummy'
 
 
 @pytest.fixture
@@ -38,6 +38,16 @@ def test_backend_is_correct(monkeypatch, restore_backend):
     )
 
 
+def test_backend_can_be_set_in_plot_call(monkeypatch, restore_backend):
+    monkeypatch.setitem(sys.modules, "pandas_dummy_backend", dummy_backend)
+    df = pandas.DataFrame([1,2,3])
+
+    assert pandas.get_option("plotting.backend") == "matplotlib"
+    assert (
+        df.plot(backend='pandas_dummy_backend') == 'used_dummy'
+    )
+
+
 @td.skip_if_no_mpl
 def test_register_entrypoint(restore_backend):