feat: Sort _ChannelSummaryMixin.channel_nbins by keys to match `cha…

…nnels` order (#1546)

* Sort _ChannelSummaryMixin.channel_nbins dict by keys to match the order of _ChannelSummaryMixin.channels
* Add a test for the order of channel_nbins keys matching the order of channels entries

src/pyhf/mixins.py

@@ -42,6 +42,9 @@ def __init__(self, *args, **kwargs):
         self.samples = sorted(list(set(self.samples)))
         self.parameters = sorted(list(set(self.parameters)))
         self.modifiers = sorted(list(set(self.modifiers)))
+        self.channel_nbins = {
+            channel: self.channel_nbins[channel] for channel in self.channels
+        }
 
         self.channel_slices = {}
         begin = 0

tests/test_mixins.py

@@ -45,3 +45,12 @@ def test_channel_summary_mixin_empty():
     assert mixin.modifiers == []
     assert mixin.parameters == []
     assert mixin.samples == []
+
+
+def test_channel_nbins_sorted_as_channels(spec):
+    assert "channels" in spec
+    spec["channels"].append(spec["channels"][0].copy())
+    spec["channels"][-1]["name"] = "a_make_first_in_sort_channel2"
+    mixin = pyhf.mixins._ChannelSummaryMixin(channels=spec["channels"])
+    assert mixin.channels == ["a_make_first_in_sort_channel2", "channel1"]
+    assert list(mixin.channel_nbins.keys()) == mixin.channels