Add regression test for histogram conversion with clamped bargap

Author: robertoffmoura

plotly/matplotlylib/tests/test_renderer.py

@@ -213,3 +213,16 @@ def test_get_bar_gap_clamps_negative_float_noise():
     assert get_bar_gap([0.0, 1.0], [1.0 + 1e-15, 2.0]) == 0.0
     # positive gaps are unchanged
     assert get_bar_gap([0.0, 2.0], [1.0, 3.0]) == 1.0
+
+
+def test_histogram_converts():
+    """Histograms must convert without error and keep bargap in plotly's
+    valid [0, 1] range; get_bar_gap can return a gap with floating point
+    noise for touching bars, which plotly rejects."""
+    fig, ax = plt.subplots()
+    ax.hist(np.random.randn(1000), 30)
+
+    plotly_fig = tls.mpl_to_plotly(fig)
+
+    assert len(plotly_fig.data) == 1
+    assert 0 <= plotly_fig.layout.bargap <= 1