Add unittest to downsample1d multi

holoviews/tests/operation/test_downsample.py

@@ -0,0 +1,20 @@
+import pytest
+
+import holoviews as hv
+from holoviews.operation.downsample import downsample1d
+
+
+@pytest.mark.parametrize("plottype", ["overlay", "ndoverlay"])
+def test_downsample1d_multi(plottype):
+    N = 1000
+    assert N > downsample1d.width
+
+    if plottype == "overlay":
+        figure = hv.Overlay([hv.Curve(range(N)), hv.Curve(range(N))])
+    elif plottype == "ndoverlay":
+        figure = hv.NdOverlay({"A": hv.Curve(range(N)), "B": hv.Curve(range(N))})
+
+    figure_values = downsample1d(figure, dynamic=False).data.values()
+    for n in figure_values:
+        for value in n.data.values():
+            assert value.size == downsample1d.width