Add support for dt.timedelta to travel class

fixes adamchainz#38

src/time_machine/__init__.py

@@ -77,6 +77,7 @@
     int,
     float,
     dt.datetime,
+    dt.timedelta,
     dt.date,
     str,
 ]
@@ -117,6 +118,12 @@ def extract_timestamp_tzname(
         if dest.tzinfo is None:
             dest = dest.replace(tzinfo=dt.timezone.utc)
         timestamp = dest.timestamp()
+    elif isinstance(dest, dt.timedelta):
+        if escape_hatch.is_travelling():
+            raise TypeError(
+                "Timedelta destination is not supported when already time travelling."
+            )
+        timestamp = time() + dest.total_seconds()
     elif isinstance(dest, dt.date):
         timestamp = dt.datetime.combine(
             dest, dt.time(0, 0), tzinfo=dt.timezone.utc

tests/test_time_machine.py

@@ -445,6 +445,28 @@ def test_destination_generator():
     assert time.time() == EPOCH + 13.0
 
 
+def test_destination_delta():
+    now = time.time()
+    with time_machine.travel(dt.timedelta(seconds=3600)):
+        assert now + 3600 < time.time() < now + 3601
+
+
+def test_destination_negative_delta():
+    now = time.time()
+    with time_machine.travel(dt.timedelta(seconds=-3600)):
+        assert now - 3600 < time.time() < now - 3599
+
+
+@time_machine.travel(0)
+def test_destination_delta_raises():
+    with pytest.raises(TypeError) as excinfo:
+        time_machine.travel(dt.timedelta(seconds=3600))
+
+    assert excinfo.value.args == (
+        "Timedelta destination is not supported when already time travelling.",
+    )
+
+
 def test_traveller_object():
     traveller = time_machine.travel(EPOCH + 10.0)
     assert time.time() >= LIBRARY_EPOCH