Add regression test for transparent line colors

Author: robertoffmoura

plotly/matplotlylib/tests/test_renderer.py

@@ -93,3 +93,13 @@ def test_boxplot_converts_with_none_marker_facecolor():
     ax.boxplot(np.random.randn(100, 4))
     plotly_fig = tls.mpl_to_plotly(fig)  # used to raise ValueError
     assert len(plotly_fig.data) > 0
+
+
+def test_line_with_none_color_converts():
+    """Lines with color='none' use the string 'none' for the line color,
+    which plotly rejects; it must be exported as a transparent line."""
+    fig, ax = plt.subplots()
+    ax.plot([0, 1], [0, 1], color="none")
+    plotly_fig = tls.mpl_to_plotly(fig)  # used to raise ValueError
+    assert len(plotly_fig.data) == 1
+    assert plotly_fig.data[0].line.color == "rgba(0,0,0,0)"