Add regression test for pydata#9134

xarray/tests/test_coding_times.py

@@ -1598,3 +1598,20 @@ def test_encode_cf_timedelta_casting_value_error(use_dask) -> None:
         assert encoded.attrs["units"] == "hours"
         decoded = conventions.decode_cf_variable("name", encoded)
         assert_equal(variable, decoded)
+
+
+@pytest.mark.parametrize("use_dask", [False, pytest.param(True, marks=requires_dask)])
+def test_encode_cf_timedelta_small_dtype_missing_value(use_dask):
+    # Regression test for GitHub issue #9134
+    timedeltas = np.array([1, 2, "NaT", 4], dtype="timedelta64[D]").astype(
+        "timedelta64[ns]"
+    )
+    encoding = dict(units="days", dtype=np.dtype("int16"), _FillValue=np.int16(-1))
+    variable = Variable(["time"], timedeltas, encoding=encoding)
+
+    if use_dask:
+        variable = variable.chunk({"time": 1})
+
+    encoded = conventions.encode_cf_variable(variable)
+    decoded = conventions.decode_cf_variable("name", encoded)
+    assert_equal(variable, decoded)