From: Antonio Valentino <antonio.valentino@tiscali.it>
Date: Sun, 14 Aug 2022 20:20:29 +0200
Subject: Use pytest instead of assay

Forwarded: not-needed
---
 skyfield/tests/test_against_horizons.py |  2 ++
 skyfield/tests/test_against_novas.py    |  4 ++++
 skyfield/tests/test_almanac_searches.py |  4 ++--
 skyfield/tests/test_api.py              | 21 +++++++++---------
 skyfield/tests/test_elementslib.py      | 14 +++++++-----
 skyfield/tests/test_io.py               |  7 +++---
 skyfield/tests/test_positions.py        |  6 ++---
 skyfield/tests/test_strs_and_reprs.py   |  2 ++
 skyfield/tests/test_timelib.py          | 39 ++++++++++++++++++++++-----------
 skyfield/tests/test_topos.py            | 24 ++++++++++++++++----
 skyfield/tests/test_units.py            | 28 +++++++++++------------
 skyfield/tests/test_vectors.py          |  6 ++---
 12 files changed, 99 insertions(+), 58 deletions(-)

diff --git a/skyfield/tests/test_against_horizons.py b/skyfield/tests/test_against_horizons.py
index da3ecfc..264dd33 100644
--- a/skyfield/tests/test_against_horizons.py
+++ b/skyfield/tests/test_against_horizons.py
@@ -6,6 +6,7 @@ from skyfield import api, framelib
 from skyfield.api import Topos
 from skyfield.constants import AU_M
 from skyfield.trigonometry import position_angle_of
+import pytest
 
 def _data_path(filename):
     return os.path.join(os.path.dirname(__file__), 'data', filename)
@@ -15,6 +16,7 @@ arcsecond = 1.0 / 60.0 / 60.0
 ra_arcsecond = 24.0 / 360.0 / 60.0 / 60.0
 meter = 1.0 / AU_M
 
+@pytest.fixture
 def ts():
     yield api.load.timescale()
 
diff --git a/skyfield/tests/test_against_novas.py b/skyfield/tests/test_against_novas.py
index 340eaa8..2cd1cc1 100644
--- a/skyfield/tests/test_against_novas.py
+++ b/skyfield/tests/test_against_novas.py
@@ -8,6 +8,7 @@ from skyfield.constants import AU_KM, AU_M
 from skyfield.data import hipparcos
 from skyfield.functions import BytesIO, length_of
 from .fixes import low_precision_ERA
+import pytest
 
 OLD_AU_KM = 149597870.691
 OLD_AU = AU_KM / OLD_AU_KM
@@ -17,6 +18,7 @@ arcsecond = 1.0 / 60.0 / 60.0
 ra_arcsecond = 24.0 / 360.0 / 60.0 / 60.0
 meter = 1.0 / AU_M
 
+@pytest.fixture
 def ts():
     yield load.timescale()
 
@@ -26,9 +28,11 @@ def compare(value, expected_value, epsilon):
     else:
         assert abs(value - expected_value) <= epsilon
 
+@pytest.fixture
 def de405():
     yield load('de405.bsp')
 
+@pytest.fixture
 def earth():
     eph = load('de405.bsp')
     yield eph[399]
diff --git a/skyfield/tests/test_almanac_searches.py b/skyfield/tests/test_almanac_searches.py
index ee3d717..017329e 100644
--- a/skyfield/tests/test_almanac_searches.py
+++ b/skyfield/tests/test_almanac_searches.py
@@ -2,7 +2,7 @@
 
 import numpy as np
 
-from assay import assert_raises
+import pytest
 from skyfield.api import load
 from skyfield.searchlib import find_discrete, find_maxima
 
@@ -30,7 +30,7 @@ def test_exception_if_step_days_is_missing():
     def f(t):
         return t.J > 0.0
     t0, t1 = make_t()
-    with assert_raises(AttributeError, 'missing a "step_days" attribute'):
+    with pytest.raises(AttributeError, match='missing a "step_days" attribute'):
         find_discrete(t0, t1, f, epsilon)
 
 def test_find_discrete_that_finds_nothing():
diff --git a/skyfield/tests/test_api.py b/skyfield/tests/test_api.py
index e3eebb3..83dfccd 100644
--- a/skyfield/tests/test_api.py
+++ b/skyfield/tests/test_api.py
@@ -1,17 +1,18 @@
 """Tests of the Skyfield `api` module and user-facing exceptions."""
 
 import numpy as np
-from assay import assert_raises
+import pytest
 from skyfield import api, positionlib
 from skyfield.api import Topos
 from skyfield.errors import EphemerisRangeError
 
+@pytest.fixture
 def ts():
     yield api.load.timescale()
 
 def test_sending_jd_that_is_not_a_julian_date():
     earth = api.load('de421.bsp')['earth']
-    with assert_raises(ValueError, r"please provide the at\(\) method"
+    with pytest.raises(ValueError, match=r"please provide the at\(\) method"
                        " with a Time instance as its argument,"
                        " instead of the value 'blah'"):
         earth.at('blah')
@@ -34,7 +35,7 @@ def test_astrometric_position_does_not_allow_altaz(ts):
     e = api.load('de421.bsp')
     o = e['earth'] + api.wgs84.latlon(36.7138, -112.2169)
     a = o.at(ts.utc(2014, 2, 9, 14, 50)).observe(e['mars'])
-    with assert_raises(ValueError, 'it is not useful to call .altaz'):
+    with pytest.raises(ValueError, match='it is not useful to call .altaz'):
         a.altaz()
 
 def test_ephemeris_contains_method(ts):
@@ -51,10 +52,10 @@ def test_exception_raised_for_dates_outside_ephemeris(ts):
     message = (
         'ephemeris segment only covers dates 1899-07-29 through 2053-10-09'
     )
-    with assert_raises(EphemerisRangeError, message) as a:
+    with pytest.raises(EphemerisRangeError, match=message) as a:
         eph['earth'].at(ts.tt(4096))
 
-    e = a.exception
+    e = a.value
     assert e.args == (message,)
     assert e.start_time.tdb == 2414864.5
     assert e.end_time.tdb == 2471184.5
@@ -114,7 +115,7 @@ def test_hadec_needs_a_longitude(ts):
     earth = e['earth']
     moon = e['moon']
     apparent = earth.at(ts.utc(2016)).observe(moon)
-    with assert_raises(ValueError, 'from a specific latitude and longitude'):
+    with pytest.raises(ValueError, match='from a specific latitude and longitude'):
         apparent.hadec()
 
 def test_altaz_needs_topos(ts):
@@ -122,12 +123,12 @@ def test_altaz_needs_topos(ts):
     earth = e['earth']
     moon = e['moon']
     apparent = earth.at(ts.utc(2016)).observe(moon).apparent()
-    with assert_raises(ValueError, 'from a specific latitude and longitude'):
+    with pytest.raises(ValueError, match='from a specific latitude and longitude'):
         apparent.altaz()
 
 def test_from_altaz_needs_topos():
     p = positionlib.ICRF([0.0, 0.0, 0.0])
-    with assert_raises(ValueError, 'to compute altitude and azimuth'):
+    with pytest.raises(ValueError, match='to compute altitude and azimuth'):
         p.from_altaz(alt_degrees=0, az_degrees=0)
 
 def test_from_altaz_parameters(ts):
@@ -136,9 +137,9 @@ def test_from_altaz_parameters(ts):
     p = usno.at(t)
     a = api.Angle(degrees=10.0)
     d = api.Distance(au=0.234)
-    with assert_raises(ValueError, 'the alt= parameter with an Angle'):
+    with pytest.raises(ValueError, match='the alt= parameter with an Angle'):
         p.from_altaz(alt='Bad value', alt_degrees=0, az_degrees=0)
-    with assert_raises(ValueError, 'the az= parameter with an Angle'):
+    with pytest.raises(ValueError, match='the az= parameter with an Angle'):
         p.from_altaz(az='Bad value', alt_degrees=0, az_degrees=0)
     p.from_altaz(alt=a, alt_degrees='bad', az_degrees=0)
     p.from_altaz(az=a, alt_degrees=0, az_degrees='bad')
diff --git a/skyfield/tests/test_elementslib.py b/skyfield/tests/test_elementslib.py
index 27747b0..f2c10f3 100644
--- a/skyfield/tests/test_elementslib.py
+++ b/skyfield/tests/test_elementslib.py
@@ -11,7 +11,9 @@ from skyfield.elementslib import (
 from skyfield.keplerlib import ele_to_vec
 from numpy import array, pi, ndarray, float64, repeat, seterr, inf, linspace
 import os
+import pytest
 
+@pytest.fixture
 def ts():
     yield load.timescale()
 
@@ -20,12 +22,12 @@ def _data_path(filename):
 
 ECLIPTIC = inertial_frames['ECLIPJ2000']
 
-ephem = load_file(_data_path('de430-2015-03-02.bsp'))
-jup_ephem = load_file(_data_path('jup310-2015-03-02.bsp'))
-io = jup_ephem['io']
-moon = ephem['moon']
-earth = ephem['earth']
-sun = ephem['sun']
+# ephem = load_file(_data_path('de430-2015-03-02.bsp'))
+# jup_ephem = load_file(_data_path('jup310-2015-03-02.bsp'))
+# io = jup_ephem['io']
+# moon = ephem['moon']
+# earth = ephem['earth']
+# sun = ephem['sun']
 
 seterr(all='raise')
 
diff --git a/skyfield/tests/test_io.py b/skyfield/tests/test_io.py
index 209cd7c..412236e 100644
--- a/skyfield/tests/test_io.py
+++ b/skyfield/tests/test_io.py
@@ -14,7 +14,7 @@ try:
 except ImportError:
     from mock import patch
 
-from assay import assert_raises
+import pytest
 from skyfield import api
 
 leap_second_text = (
@@ -23,6 +23,7 @@ leap_second_text = (
     b'    41499.0    1  7 1972       11\n'
 )
 
+@pytest.fixture
 def load():
     path = tempfile.mkdtemp()
     try:
@@ -49,7 +50,7 @@ def fake_download(load, filename, content):
 def test_build_url(load):
     url = 'https://ssd.jpl.nasa.gov/ftp/eph/planets/bsp/de421.bsp'
     assert load.build_url('de421.bsp') == url
-    with assert_raises(ValueError, 'know the URL'):
+    with pytest.raises(ValueError, match='know the URL'):
         load.build_url('unknown.kind.of.file')
 
 def test_open_in_main_directory(load):
@@ -98,7 +99,7 @@ def test_non_builtin_timescale_prefers_USNO_files(load):
 
 def test_non_builtin_timescale_tries_to_load_finals2000A_all(load):
     save_file(load, 'finals2000A.all', b'invalid data')
-    with assert_raises(IndexError):
+    with pytest.raises(IndexError):
         load.timescale(builtin=False)
 
 def test_close_of_ephemeris(load):
diff --git a/skyfield/tests/test_positions.py b/skyfield/tests/test_positions.py
index ca387bc..be2d860 100644
--- a/skyfield/tests/test_positions.py
+++ b/skyfield/tests/test_positions.py
@@ -8,7 +8,7 @@ from skyfield.positionlib import Geocentric, ICRF, ITRF_to_GCRS2, _GIGAPARSEC_AU
 from skyfield.starlib import Star
 from .fixes import low_precision_ERA
 
-from assay import assert_raises
+import pytest
 
 def test_subtraction():
     p0 = ICRF((10,20,30), (40,50,60), center=0, target=499)
@@ -21,7 +21,7 @@ def test_subtraction():
     assert tuple(p.velocity.au_per_d) == (36, 45, 54)
 
     p1.center = 1
-    with assert_raises(ValueError):
+    with pytest.raises(ValueError):
         p0 - p1
 
 def test_separation_from_on_scalar():
@@ -396,7 +396,7 @@ def test_astropy_conversion():
     assert a.obstime.fits == '2022-01-03T00:00:00.000'
 
     p = ICRF(r, t=t, center=3)
-    with assert_raises(NotImplementedError):
+    with pytest.raises(NotImplementedError):
         a = p.to_skycoord()
 
 def test_old_position_attribute():
diff --git a/skyfield/tests/test_strs_and_reprs.py b/skyfield/tests/test_strs_and_reprs.py
index 8a4768e..eabf658 100644
--- a/skyfield/tests/test_strs_and_reprs.py
+++ b/skyfield/tests/test_strs_and_reprs.py
@@ -1,6 +1,7 @@
 import textwrap
 from ..api import Topos, load, wgs84
 from ..sgp4lib import EarthSatellite
+import pytest
 
 lines = [
     'ISS (ZARYA)             ',
@@ -11,6 +12,7 @@ lines = [
 def dedent(s):
     return textwrap.dedent(s.rstrip())
 
+@pytest.fixture
 def eph():
     yield load('de421.bsp')
 
diff --git a/skyfield/tests/test_timelib.py b/skyfield/tests/test_timelib.py
index 7c9a0f8..bd3b86f 100644
--- a/skyfield/tests/test_timelib.py
+++ b/skyfield/tests/test_timelib.py
@@ -2,7 +2,7 @@ import datetime as dt_module
 import numbers
 import numpy as np
 import sys
-from assay import assert_raises
+import pytest
 from pytz import timezone
 from numpy import array, inf
 from skyfield import api
@@ -17,9 +17,9 @@ from datetime import datetime
 one_second = 1.0 / DAY_S
 epsilon = one_second * 42.0e-6  # 20.1e-6 is theoretical best precision
 
-continuous_timescale = ['tai', 'tt', 'tdb', 'ut1']
-time_scale_name = ['utc', 'tai', 'tt', 'tdb', 'ut1']
-time_value = [(1973, 1, 18, 1, 35, 37.5), 2441700.56640625]
+_continuous_timescale = ['tai', 'tt', 'tdb', 'ut1']
+_time_scale_name = ['utc', 'tai', 'tt', 'tdb', 'ut1']
+_time_value = [(1973, 1, 18, 1, 35, 37.5), 2441700.56640625]
 
 def test_timescale_with_old_fashioned_leap_second_table():
     # Skyfield no longer uses the awkward old-style leap second table,
@@ -39,6 +39,7 @@ def test_timescale_with_old_fashioned_leap_second_table():
     t = ts.tai(1970, 1, 1)
     assert t.utc == (1969, 12, 31, 23, 59, 50)
 
+@pytest.fixture
 def ts():
     yield api.load.timescale()
 
@@ -87,6 +88,9 @@ def all_kinds_of_time_array(ts):
 
     yield Time(ts, jd, fraction)
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('continuous_timescale,time_value',
+        zip(_continuous_timescale, _time_value))
 def test_time_creation_methods(ts, continuous_timescale, time_value):
     method = getattr(ts, continuous_timescale)
     if isinstance(time_value, tuple):
@@ -141,23 +145,25 @@ def test_days_overflow_correctly(ts):
 
 def test_sequence_behaviors_of_time_that_is_not_array(ts):
     t = ts.utc(2023, 4, 2)
-    with assert_raises(TypeError):
+    with pytest.raises(TypeError):
         for item in t:
             pass
     # The specific exception TypeError in the following case makes
     # Pandas inference.is_sequence() happy.
-    with assert_raises(TypeError):
+    with pytest.raises(TypeError):
         len(t)
 
 def test_time_can_be_indexed(ts):
     for t in all_kinds_of_time_array(ts):
         t[0]
 
+@pytest.mark.parametrize('time_scale_name', _time_scale_name)
 def test_is_time_iterable(ts, time_scale_name):
     t = getattr(ts, time_scale_name)(2020, 9, (25, 26))
     for item in t:
         pass
 
+@pytest.mark.skip('internet connection not available')
 def test_strftime_on_prehistoric_dates(ts_either):
     if sys.version_info <= (3,):
         return  # Python 2 time.strftime() complains about negative years
@@ -218,7 +224,7 @@ def test_tt_seconds_preserve_10_decimal_places_in_calendar_seconds(ts):
     assert c[:5] == (2020, 6, 7, 2, 2)
     assert '%.10f' % c[5] == '12.0123456789'
 
-time_params_with_array = [
+_time_params_with_array = [
     ((2018, 2019, 2020), 3, 25, 13, 1, 10),
     (2018, (3, 4, 5), 25, 13, 1, 10),
     (2018, 3, (25, 26, 27), 13, 1, 10),
@@ -227,6 +233,9 @@ time_params_with_array = [
     (2018, 3, 25, 13, 1, (10, 11, 12)),
 ]
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('time_scale_name,time_params_with_array',
+        zip(_time_scale_name, _time_params_with_array))
 def test_time_creation_with_arrays(ts, time_scale_name, time_params_with_array):
     print(time_scale_name)
     t = getattr(ts, time_scale_name)(*time_params_with_array)
@@ -240,9 +249,9 @@ def test_timescale_utc_method_with_array_inside(ts):
         assert t.tai[i] == ts.utc(1973, 12, 29, 23, 59, second).tai
 
 def test_that_building_time_from_naive_datetime_raises_exception(ts):
-    with assert_raises(ValueError) as info:
+    with pytest.raises(ValueError) as info:
         ts.from_datetime(datetime(1973, 12, 29, 23, 59, 48))
-    assert 'import timezone' in str(info.exception)
+    assert 'import timezone' in str(info.value)
 
 def test_building_time_from_single_utc_datetime(ts):
     t = ts.from_datetime(datetime(1973, 12, 29, 23, 59, 48, tzinfo=utc))
@@ -346,6 +355,7 @@ def test_slicing_time(ts):
     assert (t.ut1[2:4] == t24.ut1).all()
     assert (t.delta_t[2:4] == t24.delta_t).all()
 
+@pytest.mark.skip('internet connection not available')
 def test_early_utc(ts_either):
     ts = ts_either
     t = ts.utc(1915, 12, 2, 3, 4, 5.6786786)
@@ -404,22 +414,22 @@ def test_utc_datetime_exception_for_negative_year():
     ts = api.load.timescale()
     ts.julian_calendar_cutoff = GREGORIAN_START
     t = ts.utc(-1, 1, 1)
-    with assert_raises(ValueError, 'negative years like the year -1'):
+    with pytest.raises(ValueError, match='negative years like the year -1'):
         t.utc_datetime()
 
     t = ts.utc([-2, -3, -1], 1, 1)
-    with assert_raises(ValueError, 'negative years like the year -2'):
+    with pytest.raises(ValueError, match='negative years like the year -2'):
         t.utc_datetime()
 
 def test_utc_datetime_exception_for_julian_leap_day():
     ts = api.load.timescale()
     ts.julian_calendar_cutoff = GREGORIAN_START
     t = ts.utc(700, 2, 29)
-    with assert_raises(ValueError, 'Julian leap days like 700 February 29'):
+    with pytest.raises(ValueError, match='Julian leap days like 700 February 29'):
         t.utc_datetime()
 
     t = ts.utc(700, 2, [28, 29, 30])
-    with assert_raises(ValueError, 'Julian leap days like 700 February 29'):
+    with pytest.raises(ValueError, match='Julian leap days like 700 February 29'):
         t.utc_datetime()
 
 def test_iso_of_decimal_that_rounds_up(ts):
@@ -693,6 +703,7 @@ def test_raw_julian_gregorian_cutover():
         2299159, 2299160, 2299161, 2299162,
     ]
 
+@pytest.mark.parametrize('time_scale_name', _time_scale_name)
 def test_constructor_julian_gregorian_cutover(time_scale_name):
     if sys.version_info <= (3,):
         return  # Python 2 time.strftime() complains about the year 1582
@@ -724,6 +735,7 @@ def test_constructor_julian_gregorian_cutover(time_scale_name):
     assert jd(1752, 9, 2) == 2361220.5
     assert jd(1752, 9, 14) == 2361221.5
 
+@pytest.mark.parametrize('time_scale_name', _time_scale_name)
 def test_calendar_tuple_julian_gregorian_cutover(time_scale_name):
     if sys.version_info <= (3,):
         return  # Python 2 time.strftime() complains about the year 1582
@@ -755,6 +767,7 @@ def test_calendar_tuple_julian_gregorian_cutover(time_scale_name):
     assert ymd(2361220.5) == (1752, 9, 2)
     assert ymd(2361221.5) == (1752, 9, 14)
 
+@pytest.mark.parametrize('time_scale_name', _time_scale_name)
 def test_strftime_julian_gregorian_cutover(time_scale_name):
     if sys.version_info <= (3,):
         return  # Python 2 time.strftime() complains about the year 1582
diff --git a/skyfield/tests/test_topos.py b/skyfield/tests/test_topos.py
index d292edb..7fc1e34 100644
--- a/skyfield/tests/test_topos.py
+++ b/skyfield/tests/test_topos.py
@@ -1,4 +1,4 @@
-from assay import assert_raises
+import pytest
 from numpy import abs, arange, sqrt
 
 from skyfield import constants
@@ -7,16 +7,19 @@ from skyfield.functions import length_of
 from skyfield.positionlib import Apparent, Barycentric
 from skyfield.toposlib import ITRSPosition, iers2010
 
-angle = (-15, 15, 35, 45)
+_angle = (-15, 15, 35, 45)
 
+@pytest.fixture
 def ts():
     yield load.timescale()
 
-def t():
+def _t_gen():
     ts = load.timescale()
     yield ts.utc(2020, 11, 3, 17, 5)
     yield ts.utc(2020, 11, 3, 17, [5, 5])
 
+_t = list(_t_gen())
+
 def test_polar_radius():
     assert round(wgs84.polar_radius.km) == 6357
 
@@ -144,14 +147,18 @@ def test_polar_motion_when_computing_altaz_coordinates(ts):
     assert abs(alt.degrees - novas_alt) < 1.9e-9
     assert abs(az.degrees - novas_az) < 1.3e-7
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('angle', _angle)
 def test_subpoint_with_wrong_center(ts, angle):
     t = ts.utc(2020, 12, 31)
     p = Barycentric([0,0,0], t=t)
-    with assert_raises(ValueError, 'you can only calculate a geographic'
+    with pytest.raises(ValueError, match='you can only calculate a geographic'
                        ' position from a position which is geocentric'
                        ' .center=399., but this position has a center of 0'):
         wgs84.subpoint(p)
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('angle', _angle)
 def test_iers2010_subpoint(ts, angle):
     t = ts.utc(2018, 1, 19, 14, 37, 55)
     # An elevation of 0 is more difficult for the routine's accuracy
@@ -168,6 +175,8 @@ def test_iers2010_subpoint(ts, angle):
     error_mas = 60.0 * 60.0 * 1000.0 * error_degrees
     assert error_mas < 0.1
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('angle', _angle)
 def test_wgs84_subpoint(ts, angle):
     t = ts.utc(2018, 1, 19, 14, 37, 55)
     # An elevation of 0 is more difficult for the routine's accuracy
@@ -184,6 +193,7 @@ def test_wgs84_subpoint(ts, angle):
     error_mas = 60.0 * 60.0 * 1000.0 * error_degrees
     assert error_mas < 0.1
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
 def test_wgs84_subpoint_at_pole(ts):
     # The `height` previously suffered from very low precision at the pole.
     t = ts.utc(2023, 4, 7, 12, 44)
@@ -196,6 +206,8 @@ def test_wgs84_subpoint_at_pole(ts):
     g = wgs84.geographic_position_of(p)
     assert abs(g.elevation.m - 10.0) < micrometer
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('angle', _angle)
 def test_wgs84_round_trip_with_polar_motion(ts, angle):
     t = ts.utc(2018, 1, 19, 14, 37, 55)
     ts.polar_motion_table = [0.0], [0.003483], [0.358609]
@@ -212,6 +224,8 @@ def test_wgs84_round_trip_with_polar_motion(ts, angle):
     error_mas = 60.0 * 60.0 * 1000.0 * error_degrees
     assert error_mas < 0.1
 
+@pytest.mark.parametrize('t', _t)
+@pytest.mark.parametrize('angle', _angle)
 def test_latlon_and_subpoint_methods(t, angle):
     g = wgs84.latlon(angle, 2 * angle, elevation_m=1234.0)
     pos = g.at(t)
@@ -253,6 +267,8 @@ def test_latlon_and_subpoint_methods(t, angle):
     assert g2.elevation.m == 0.0
     check_itrs(g2.itrs_xyz.m, 1234.0)
 
+@pytest.mark.parametrize('ts', [ts], indirect=True)
+@pytest.mark.parametrize('angle', _angle)
 def test_deprecated_position_subpoint_method(ts, angle):
     t = ts.utc(2018, 1, 19, 14, 37, 55)
     top = iers2010.latlon(angle, angle, elevation_m=0.0)
diff --git a/skyfield/tests/test_units.py b/skyfield/tests/test_units.py
index 7a418e4..fb5ce55 100644
--- a/skyfield/tests/test_units.py
+++ b/skyfield/tests/test_units.py
@@ -1,6 +1,6 @@
 """Tests of whether units behave."""
 
-from assay import assert_raises
+import pytest
 from numpy import array, nan
 from skyfield.units import (
     Angle, Distance, Velocity, UnpackingError, WrongUnitError,
@@ -61,7 +61,7 @@ def test_angle_array_strs():
     assert str(h) == '3 values from 00h 30m 00.00s to -13h 00m 00.00s'
     assert str(d) == '''3 values from 07deg 30' 00.0" to -195deg 00' 00.0"'''
 
-    with assert_raises(WrongUnitError):
+    with pytest.raises(WrongUnitError):
         h.dstr()
         d.hstr()
 
@@ -142,13 +142,13 @@ to use this Distance, ask for its value in a particular unit:
     distance.km
     distance.m'''
 
-    with assert_raises(UnpackingError) as a:
+    with pytest.raises(UnpackingError) as a:
         x, y, z = distance
-    assert str(a.exception) == expect
+    assert str(a.value) == expect
 
-    with assert_raises(UnpackingError) as a:
+    with pytest.raises(UnpackingError) as a:
         distance[0]
-    assert str(a.exception) == expect
+    assert str(a.value) == expect
 
     velocity = Velocity(1.234)
     expect = '''\
@@ -158,13 +158,13 @@ to use this Velocity, ask for its value in a particular unit:
     velocity.km_per_s
     velocity.m_per_s'''
 
-    with assert_raises(UnpackingError) as a:
+    with pytest.raises(UnpackingError) as a:
         x, y, z = velocity
-    assert str(a.exception) == expect
+    assert str(a.value) == expect
 
-    with assert_raises(UnpackingError) as a:
+    with pytest.raises(UnpackingError) as a:
         velocity[0]
-    assert str(a.exception) == expect
+    assert str(a.value) == expect
 
     angle = Angle(radians=1.234)
     expect = '''\
@@ -174,13 +174,13 @@ to use this Angle, ask for its value in a particular unit:
     angle.hours
     angle.radians'''
 
-    with assert_raises(UnpackingError) as a:
+    with pytest.raises(UnpackingError) as a:
         x, y, z = angle
-    assert str(a.exception) == expect
+    assert str(a.value) == expect
 
-    with assert_raises(UnpackingError) as a:
+    with pytest.raises(UnpackingError) as a:
         angle[0]
-    assert str(a.exception) == expect
+    assert str(a.value) == expect
 
 def test_constructors_accept_plain_lists():
     Distance(au=[1,2,3])
diff --git a/skyfield/tests/test_vectors.py b/skyfield/tests/test_vectors.py
index 1fca5ec..db67c0d 100644
--- a/skyfield/tests/test_vectors.py
+++ b/skyfield/tests/test_vectors.py
@@ -1,6 +1,6 @@
 # Test the behavior of all combinations of vector.
 
-from assay import assert_raises
+import pytest
 from skyfield.api import Topos, load
 from skyfield.positionlib import Geocentric
 
@@ -8,14 +8,14 @@ def test_bad_addition():
     planets = load('de421.bsp')
     earth = planets['earth']
     mars = planets['mars']
-    with assert_raises(ValueError, 'the center where the other vector starts'):
+    with pytest.raises(ValueError, match='the center where the other vector starts'):
         earth + mars
 
 def test_bad_subtraction():
     planets = load('de421.bsp')
     earth = planets['earth']
     usno = Topos('38.9215 N', '77.0669 W', elevation_m=92.0)
-    with assert_raises(ValueError, 'if they both start at the same center'):
+    with pytest.raises(ValueError, match='if they both start at the same center'):
         earth - usno
 
 def test_chebyshev_subtraction():