.

specreduce/tests/test_tracing.py

@@ -2,6 +2,8 @@
 import pytest
 
 from astropy.modeling import models
+from astropy.nddata import NDData
+import astropy.units as u
 from specreduce.utils.synth_data import make_2d_trace_image
 from specreduce.tracing import Trace, FlatTrace, ArrayTrace, FitTrace
 
@@ -148,4 +150,14 @@ def test_fit_trace():
     with pytest.raises(ValueError, match=r'image is fully masked'):
         FitTrace(img_all_nans)
 
-    # could try to catch warning thrown for all-nan bins
+    # test that warning is raised when many bins are masked
+    mask = np.zeros(img.shape)
+    mask[:, 75:76] = 1
+    nddat = NDData(data=img, mask=mask, unit=u.DN)
+    warn_bins = np.arange(20)
+    warn_bins = ', '.join([str(x) for x in warn_bins])
+    msg = f"All pixels in bin 75 are masked. Falling to trace value from all-bin fit."
+    with pytest.warns(UserWarning, match=msg):
+        FitTrace(nddat)
+
+    # could try to catch warning thrown for all-nan bins

specreduce/tracing.py

@@ -349,13 +349,13 @@ def __post_init__(self):
 
         # warn about fully-masked bins
         if len(warn_bins) > 0:
-            plural = 's' if len(warn_bins) == 1 else ''
+            plural = 's' if len(warn_bins) > 1 else ''
             # if there are a ton of bins, we don't want to print them all out
+            print(warn_bins)
             if len(warn_bins) > 20:
                 warn_bins = warn_bins[0: 10] + ['...'] + warn_bins[10: 19]
-
-            warnings.warn(f"All pixels in bin{plural} {', '.join([str(x) for x in warn_bins])} are masked. Falling "
-                              'to trace value from all-bin fit.')
+            warnings.warn(f"All pixels in bin{plural} {', '.join([str(x) for x in warn_bins])}"
+                            " are masked. Falling to trace value from all-bin fit.")
 
         # recenter bin positions
         x_bins = (x_bins[:-1] + x_bins[1:]) / 2