Add test

panel/tests/io/test_save.py

@@ -0,0 +1,32 @@
+from io import StringIO
+
+from panel.pane import Vega
+from panel.models.vega import VegaPlot
+
+
+vega_example = {
+    'config': {
+        'mark': {'tooltip': None},
+        'view': {'height': 300, 'width': 400}
+    },
+    'data': {'values': [{'x': 'A', 'y': 5},
+                        {'x': 'B', 'y': 3},
+                        {'x': 'C', 'y': 6},
+                        {'x': 'D', 'y': 7},
+                        {'x': 'E', 'y': 2}]},
+    'mark': 'bar',
+    'encoding': {'x': {'type': 'ordinal', 'field': 'x'},
+                 'y': {'type': 'quantitative', 'field': 'y'}},
+    '$schema': 'https://vega.github.io/schema/vega-lite/v3.2.1.json'
+}
+
+
+def test_save_external():
+    sio = StringIO()
+    pane = Vega(vega_example)
+
+    pane.save(sio)
+    sio.seek(0)
+    html = sio.read()
+    for js in VegaPlot.__javascript_raw__:
+        assert js in html