add tests for check_plots()

Author: afeld

extras/test_autograder_helpers.py

@@ -0,0 +1,19 @@
+import pytest
+from .autograder.source.tests.helpers import check_plots
+
+
+def test_check_plots_good():
+    check_plots('px.line(df, x="year", y="life_expectancy", title="Life expectancy")')
+
+
+def test_check_plots_get_trendline_results():
+    check_plots("px.get_trendline_results(fig)")
+
+
+def test_check_plots_no_plotly():
+    check_plots("")
+
+
+def test_check_plots_no_title():
+    with pytest.raises(AssertionError):
+        check_plots('px.line(df, x="year", y="life_expectancy")')