add tests

xarray/tests/test_cftimeindex.py

@@ -241,6 +241,28 @@ def test_cftimeindex_field_accessors(index, field, expected):
     assert_array_equal(result, expected)
 
 
+@requires_cftime
+@pytest.mark.parametrize(
+    ("field"),
+    [
+        "year",
+        "month",
+        "day",
+        "hour",
+        "minute",
+        "second",
+        "microsecond",
+        "dayofyear",
+        "dayofweek",
+        "days_in_month",
+    ],
+)
+def test_empty_cftimeindex_field_accessors(field):
+    index = CFTimeIndex([])
+    result = getattr(index, field)
+    assert_array_equal(result, np.array([], dtype=np.float64))
+
+
 @requires_cftime
 def test_cftimeindex_dayofyear_accessor(index):
     result = index.dayofyear
@@ -959,6 +981,31 @@ def test_cftimeindex_calendar_property(calendar, expected):
     assert index.calendar == expected
 
 
+@requires_cftime
+def test_empty_cftimeindex_calendar_property():
+    index = CFTimeIndex([])
+    assert index.calendar is None
+
+
+@requires_cftime
+@pytest.mark.parametrize(
+    "calendar",
+    [
+        "noleap",
+        "365_day",
+        "360_day",
+        "julian",
+        "gregorian",
+        "standard",
+        "proleptic_gregorian",
+    ],
+)
+def test_cftimeindex_freq_property_none_size_lt_3(calendar):
+    for periods in range(3):
+        index = xr.cftime_range(start="2000", periods=periods, calendar=calendar)
+        assert index.freq is None
+
+
 @requires_cftime
 @pytest.mark.parametrize(
     ("calendar", "expected"),
@@ -1152,6 +1199,18 @@ def test_rounding_methods_against_datetimeindex(freq, method):
     assert result.equals(expected)
 
 
+@requires_cftime
+@pytest.mark.parametrize("method", ["floor", "ceil", "round"])
+def test_rounding_methods_empty_cftimindex(method):
+    index = CFTimeIndex([])
+    result = getattr(index, method)("2s")
+
+    expected = CFTimeIndex([])
+
+    assert result.equals(expected)
+    assert result is not index
+
+
 @requires_cftime
 @pytest.mark.parametrize("method", ["floor", "ceil", "round"])
 def test_rounding_methods_invalid_freq(method):
@@ -1230,6 +1289,14 @@ def test_asi8_distant_date():
     np.testing.assert_array_equal(result, expected)
 
 
+@requires_cftime
+def test_asi8_empty_cftimeindex():
+    index = xr.CFTimeIndex([])
+    result = index.asi8
+    expected = np.array([], dtype=int)
+    np.testing.assert_array_equal(result, expected)
+
+
 @requires_cftime
 def test_infer_freq_valid_types():
     cf_indx = xr.cftime_range("2000-01-01", periods=3, freq="D")