Add a second test and update release notes

doc/releases/v0.12.0.txt

@@ -55,6 +55,8 @@ Other updates
 
 - |Fix| Fixed a regression in 0.11.2 that caused some functions to stall indefinitely or raise when the input data had a duplicate index (:pr:`2776`).
 
+- |Fix| Fixed two edgecases in :func:`histplot` when only `binwidth` was provided (:pr:`2813').
+
 - |Fix| In :func:`lineplot`, allowed the `dashes` keyword to set the style of a line without mapping a `style` variable (:pr:`2449`).
 
 - |Dependencies| Made `scipy` an optional dependency and added `pip install seaborn[all]` as a method for ensuring the availability of compatible `scipy` and `statsmodels` libraries at install time. This has a few minor implications for existing code, which are explained in the Github pull request (:pr:`2398`).

seaborn/tests/test_statistics.py

@@ -289,6 +289,12 @@ def test_odd_single_observation(self):
         assert len(h) == 1
         assert (e[1] - e[0]) == pytest.approx(.03)
 
+    def test_binwidth_roundoff(self):
+        # GH2785
+        x = np.array([2.4, 2.5, 2.6])
+        h, e = Histogram(binwidth=0.01)(x)
+        assert h.sum() == 3
+
     def test_histogram(self, x):
 
         h = Histogram()