Add datetime encode/decode property test

properties/test_encode_decode.py

@@ -15,7 +15,8 @@
 from hypothesis import given
 
 import xarray as xr
-from xarray.testing.strategies import variables
+from xarray.testing.strategies import cftime_arrays, variables
+from xarray.tests import requires_cftime
 
 
 @pytest.mark.slow
@@ -43,3 +44,28 @@
     coder = xr.coding.variables.CFScaleOffsetCoder()
     roundtripped = coder.decode(coder.encode(original))
     xr.testing.assert_identical(original, roundtripped)
+
+
+@requires_cftime
+@given(original_array=cftime_arrays(shapes=npst.array_shapes(max_dims=1)))
+def test_CFDatetime_coder_roundtrip_cftime(original_array) -> None:
+    original = xr.Variable("time", original_array)
+    coder = xr.coding.times.CFDatetimeCoder(use_cftime=True)
+    roundtripped = coder.decode(coder.encode(original))
+    xr.testing.assert_identical(original, roundtripped)
+
+
+@given(
+    original_array=npst.arrays(
+        dtype=npst.datetime64_dtypes(endianness="=", max_period="ns"),
+        shape=npst.array_shapes(max_dims=1),
+    )
+)
+def test_CFDatetime_coder_roundtrip_numpy(original_array) -> None:
+    original = xr.Variable("time", original_array)
+    coder = xr.coding.times.CFDatetimeCoder(use_cftime=False)
+    roundtripped = coder.decode(coder.encode(original))
+    xr.testing.assert_identical(original, roundtripped)
+
+
+# datetime_arrays =, shape=npst.array_shapes(min_dims=1, max_dims=1)) | cftime_arrays()

xarray/testing/strategies.py

@@ -135,6 +135,60 @@ def dimension_names(
     )
 
 
+calendars = st.sampled_from(
+    [
+        "standard",
+        "gregorian",
+        "proleptic_gregorian",
+        "noleap",
+        "365_day",
+        "360_day",
+        "julian",
+        "all_leap",
+        "366_day",
+    ]
+)
+
+
+@st.composite
+def cftime_units(draw: st.DrawFn, *, calendar: str) -> str:
+    choices = ["days", "hours", "minutes", "seconds", "milliseconds", "microseconds"]
+    if calendar == "360_day":
+        choices += ["months"]
+    elif calendar == "noleap":
+        choices += ["common_years"]
+    time_units = draw(st.sampled_from(choices))
+
+    dt = draw(st.datetimes())
+    year, month, day = dt.year, dt.month, dt.day
+    if calendar == "360_day":
+        day = min(day, 30)
+    if calendar in ["360_day", "365_day", "noleap"] and month == 2 and day == 29:
+        day = 28
+
+    return f"{time_units} since {year}-{month}-{day}"
+
+
+@st.composite
+def cftime_arrays(
+    draw: st.DrawFn,
+    *,
+    shapes: st.SearchStrategy[tuple[int, ...]] = npst.array_shapes(),
+    calendars: st.SearchStrategy[str] = calendars,
+    elements: dict[str, Any] | None = None,
+) -> np.ndarray[Any, Any]:
+    import cftime
+
+    if elements is None:
+        elements = {}
+    elements.setdefault("min_value", 0)
+    elements.setdefault("max_value", 10_000)
+    cal = draw(calendars)
+    values = draw(npst.arrays(dtype=np.int64, shape=shapes, elements=elements))
+    unit = draw(cftime_units(calendar=cal))
+    return cftime.num2date(values, units=unit, calendar=cal)
+
+
 def dimension_sizes(
     *,
     dim_names: st.SearchStrategy[Hashable] = names(),