improve comments in test

tests/instruments/test_ship_underwater_st.py

@@ -7,20 +7,25 @@
 from virtual_ship.instruments.ship_underwater_st import simulate_ship_underwater_st
 import xarray as xr
 from typing import Callable
-from datetime import timedelta
 
 
 def test_simulate_ship_underwater_st(tmp_dir_factory: Callable[[str], str]) -> None:
+    # depth at which the sampling will be done
     DEPTH = -2
 
+    # arbitrary time offset for the dummy fieldset
     base_time = np.datetime64("1950-01-01")
 
+    # variabes we are going to compare between expected and actual observations
     variables = ["salinity", "temperature", "lat", "lon"]
 
+    # were to sample
     sample_points = [
         Spacetime(Location(3, 0), base_time + np.timedelta64(0, "s")),
         Spacetime(Location(7, 0), base_time + np.timedelta64(1, "s")),
     ]
+
+    # expected observations at sample points
     expected_obs = [
         {"salinity": 1, "temperature": 2, "lat": 3, "lon": 0, "time": base_time},
         {
@@ -32,6 +37,7 @@ def test_simulate_ship_underwater_st(tmp_dir_factory: Callable[[str], str]) -> N
         },
     ]
 
+    # create fieldset based on the expected observations
     fieldset = FieldSet.from_data(
         {
             "U": np.zeros((2, 2)),
@@ -63,10 +69,14 @@ def test_simulate_ship_underwater_st(tmp_dir_factory: Callable[[str], str]) -> N
 
     results = xr.open_zarr(out_file_name)
 
-    assert len(results.trajectory) == 1
+    # below we assert if output makes sense
+    assert len(results.trajectory) == 1  # expect a singe trajectory
     traj = results.trajectory.item()
-    assert len(results.sel(trajectory=traj).obs) == len(sample_points)
+    assert len(results.sel(trajectory=traj).obs) == len(
+        sample_points
+    )  # expect as many obs as sample points
 
+    # for every obs, check if the variables match the expected observations
     for i, (obs_i, exp) in enumerate(
         zip(results.sel(trajectory=traj).obs, expected_obs, strict=True)
     ):