Fix unit label handling

docs/iris/src/whatsnew/3.0.rst

@@ -168,6 +168,7 @@ This document explains the changes made to Iris for this release
   Previously, the first tick label would occasionally be duplicated. This also
   removes the use of Matplotlib's deprecated ``IndexFormatter``. (:pull:`3857`)
 
+* `@znicholls`_ fixed :meth:`~iris.quickplot._title` to only check ``units.is_time_reference`` if the ``units`` symbol is not used. (:pull:`3902`)
 
 .. _whatsnew 3.0 changes:
 
@@ -417,6 +418,9 @@ This document explains the changes made to Iris for this release
 * `@owena11`_ identified and optimised a bottleneck in ``FieldsFile`` header
   loading due to the use of :func:`numpy.fromfile`. (:pull:`3791`)
 
+* `@znicholls`_ added a test for plotting with the label being taken from the unit's symbol, see :meth:`~iris.tests.test_quickplot.TestLabels.test_pcolormesh_str_symbol` (:pull:`3902`).
+
+* `@znicholls`_ made :func:`~iris.tests.idiff.step_over_diffs` robust to hyphens (``-``) in the input path (i.e. the ``result_dir`` argument) (:pull:`3902`).
 
 .. _Read the Docs: https://scitools-iris.readthedocs.io/en/latest/
 .. _Matplotlib: https://matplotlib.org/
@@ -450,6 +454,7 @@ This document explains the changes made to Iris for this release
 .. _@rcomer: https://github.com/rcomer
 .. _@jvegasbsc: https://github.com/jvegasbsc
 .. _@zklaus: https://github.com/zklaus
+.. _@znicholls: https://github.com/znicholls
 .. _ESMValTool: https://github.com/ESMValGroup/ESMValTool
 .. _v75: https://cfconventions.org/Data/cf-standard-names/75/build/cf-standard-name-table.html
 .. _sphinx-panels: https://sphinx-panels.readthedocs.io/en/latest/

lib/iris/quickplot.py

@@ -49,7 +49,7 @@ def _title(cube_or_coord, with_units):
 
             if _use_symbol(units):
                 units = units.symbol
-            if units.is_time_reference():
+            elif units.is_time_reference():
                 # iris.plot uses matplotlib.dates.date2num, which is fixed to the below unit.
                 if version.parse(_mpl_version) >= version.parse("3.3"):
                     days_since = "1970-01-01"

lib/iris/tests/idiff.py

@@ -220,7 +220,9 @@ def step_over_diffs(result_dir, action, display=True):
         count = len(results)
 
         for count_index, result_fname in enumerate(results):
-            key = os.path.splitext("-".join(result_fname.split("-")[1:]))[0]
+            key = os.path.splitext(
+                "-".join(result_fname.split("result-")[1:])
+            )[0]
             try:
                 # Calculate the test result perceptual image hash.
                 phash = imagehash.phash(

lib/iris/tests/results/imagerepo.json

@@ -908,6 +908,9 @@
         "https://scitools.github.io/test-iris-imagehash/images/v4/bb433d4e94a4c6b9c15adaadc1fb6a469c8de43a3e07904e5f016b57984e1ea1.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f3f81c07e3fa12da1c27e3f80.png"
     ],
+    "iris.tests.test_quickplot.TestLabels.test_pcolormesh_str_symbol.0": [
+        "https://scitools.github.io/test-iris-imagehash/images/v4/eea16affc05ab500956e974ac53f3d80925ac03f3f80c07e3fa12da1c27f3f80.png"
+    ],
     "iris.tests.test_quickplot.TestQuickplotCoordinatesGiven.test_non_cube_coordinate.0": [
         "https://scitools.github.io/test-iris-imagehash/images/v4/fa816a85857a955ae17e957ec57e7a81855fc17e3a81c57e1a813a85c57a1a05.png",
         "https://scitools.github.io/test-iris-imagehash/images/v4/fe816a85857a957ac07f957ac07f3e80956ac07f3e80c07f3e813e85c07e3f80.png"

lib/iris/tests/test_quickplot.py

@@ -201,6 +201,13 @@ def test_pcolormesh(self):
 
         self.check_graphic()
 
+    def test_pcolormesh_str_symbol(self):
+        pcube = self._small().copy()
+        pcube.coords("level_height")[0].units = "centimeters"
+        qplt.pcolormesh(pcube)
+
+        self.check_graphic()
+
     def test_map(self):
         cube = self._slice(["grid_latitude", "grid_longitude"])
         qplt.contour(cube)