Add extra test to check halfpoint

Co-authored-by: Chris Havlin <chris.havlin@gmail.com>

Author: cphyc

yt/data_objects/tests/test_time_series.py

@@ -148,3 +148,8 @@ def test_get_by_key(FakeDataset, fake_datasets):
 
     with pytest.raises(ValueError):
         ts.get_by_redshift(1000, tolerance=0.1)
+
+    zmid = (ts[0].current_redshift + ts[1].current_redshift) / 2
+
+    assert sfile_list[1] == ts.get_by_redshift(zmid, prefer="smaller").filename
+    assert sfile_list[0] == ts.get_by_redshift(zmid, prefer="larger").filename

yt/data_objects/time_series.py

@@ -513,6 +513,7 @@ def _get_by_attribute(
             iM = (iR + iL) // 2
             dsM = self[iM]
             vM = getattr(dsM, attribute)
+
             if sign * value < sign * vM:
                 iR = iM
                 dsR = dsM