TST: increase coverage of asfreq (#53861)

* TST: increase coverage of asfreq

* remove redundant argument

Author: natmokval

pandas/tests/frame/methods/test_asfreq.py

@@ -211,3 +211,12 @@ def test_asfreq_after_normalize(self, unit):
         )
         expected = DatetimeIndex(["2000-01-01", "2000-01-02"], freq="D").as_unit(unit)
         tm.assert_index_equal(result, expected)
+
+    def test_asfreq_2M(self):
+        index = date_range("1/1/2000", periods=6, freq="M")
+        df = DataFrame({"s": Series([0.0, 1.0, 2.0, 3.0, 4.0, 5.0], index=index)})
+        expected = df.asfreq(freq="2M")
+
+        index = date_range("1/1/2000", periods=3, freq="2M")
+        result = DataFrame({"s": Series([0.0, 2.0, 4.0], index=index)})
+        tm.assert_frame_equal(result, expected)