Add a test for the new repeated stepper

tests/test_repeated_stepper.py

@@ -0,0 +1,28 @@
+import jax
+import pytest
+
+import exponax as ex
+
+
+def test_repeated_stepper():
+    DOMAIN_EXTENT = 1.0
+    NUM_POINTS = 81
+    DT = 0.1
+    NUM_REPEATS = 10
+
+    burgers_stepper = ex.stepper.Burgers(1, DOMAIN_EXTENT, NUM_POINTS, DT)
+
+    burgers_stepper_repeated = ex.RepeatedStepper(burgers_stepper, NUM_REPEATS)
+
+    burgers_stepper_repeated_manually = ex.repeat(burgers_stepper, NUM_REPEATS)
+
+    u_0 = ex.ic.RandomTruncatedFourierSeries(1, max_one=True)(
+        NUM_POINTS, key=jax.random.PRNGKey(0)
+    )
+
+    u_final = burgers_stepper_repeated(u_0)
+    u_final_manually = burgers_stepper_repeated_manually(u_0)
+
+    # Need a looser rel tolerance because Burgers is a decaying phenomenon,
+    # hence the expected/reference state has low magnitude after 10 steps.
+    assert u_final == pytest.approx(u_final_manually, rel=1e-3)