TST: Add test to verify 'dropna' behaviour on SparseArray (#34879)

Author: MBrouns

pandas/tests/arrays/sparse/test_array.py

@@ -1295,3 +1295,15 @@ def test_map_missing():
 
     result = arr.map({0: 10, 1: 11})
     tm.assert_sp_array_equal(result, expected)
+
+
+@pytest.mark.parametrize("fill_value", [np.nan, 1])
+def test_dropna(fill_value):
+    # GH-28287
+    arr = SparseArray([np.nan, 1], fill_value=fill_value)
+    exp = SparseArray([1.0], fill_value=fill_value)
+    tm.assert_sp_array_equal(arr.dropna(), exp)
+
+    df = pd.DataFrame({"a": [0, 1], "b": arr})
+    expected_df = pd.DataFrame({"a": [1], "b": exp}, index=pd.Int64Index([1]))
+    tm.assert_equal(df.dropna(), expected_df)