Unify time function names, add test

src/ctapipe_io_zfits/conftest.py

@@ -9,7 +9,7 @@
 from protozfits.CTA_DL0_Subarray_pb2 import DataStream, Event
 from protozfits.CoreMessages_pb2 import AnyArray
 
-from ctapipe_io_zfits.time import time_to_cta_high
+from ctapipe_io_zfits.time import time_to_cta_high_res
 
 ANY_ARRAY_TYPE_TO_NUMPY_TYPE = {
     1: np.int8,
@@ -108,7 +108,7 @@ def dummy_dl0(dl0_base):
         trigger_file.move_to_new_table("Events")
 
         for event_id in range(1, 101):
-            time_s, time_qns = time_to_cta_high(time)
+            time_s, time_qns = time_to_cta_high_res(time)
             trigger_file.write_message(Event(
                 event_id=event_id,
                 trigger_type=1,

src/ctapipe_io_zfits/tests/test_time.py

@@ -0,0 +1,37 @@
+from astropy.time import Time
+import astropy.units as u
+import numpy as np
+import pytest
+
+roundtrip_times = [
+    '2020-01-01T00:00:00.12345678925',
+    '2020-01-01T00:00:00.1234567895',
+    '2020-01-01T00:00:00.12345678975',
+    '2020-01-01T00:00:00.123456790',
+]
+
+@pytest.mark.parametrize("timestamp", roundtrip_times)
+def test_cta_high_round_trip(timestamp):
+    from ctapipe_io_zfits.time import time_to_cta_high_res, cta_high_res_to_time
+
+    # note: precision=9 only affects text conversion, not actual precision
+    time = Time(timestamp, scale='tai', precision=9)
+    seconds, quarter_nanoseconds = time_to_cta_high_res(time)
+    time_back = cta_high_res_to_time(seconds, quarter_nanoseconds)
+
+    roundtrip_error = (time - time_back).to_value(u.ns)
+    np.testing.assert_almost_equal(roundtrip_error, 0.0)
+
+
+test_data = [
+    (Time(0, 12.25e-9, format='unix_tai'), 0, 49),
+    (Time(12345, 12.25e-9, format='unix_tai'), 12345, 49),
+]
+
+@pytest.mark.parametrize("time,expected_s,expected_qns", test_data)
+def test_cta_time_to_cta_high_res(time, expected_s, expected_qns):
+    from ctapipe_io_zfits.time import time_to_cta_high_res
+
+    seconds, quarter_nanoseconds = time_to_cta_high_res(time)
+    assert seconds == expected_s
+    assert quarter_nanoseconds == expected_qns

src/ctapipe_io_zfits/time.py

@@ -32,7 +32,7 @@ def to_seconds(days):
     return np.divmod(seconds, 1)
 
 
-def time_to_cta_high(time):
+def time_to_cta_high_res(time):
     '''Convert astropy Time to cta high precision timestamp'''
     # make sure we are in TAI
     time = time.tai