separated out plot tests into external tests and added test for informative error message

Author: stringertheory

tests/test_plot.py

@@ -1,38 +1,28 @@
+import importlib
+
 import pytest
 
 import traces
 
-
-@pytest.mark.mpl_image_compare(
-    savefig_kwargs={"bbox_inches": "tight", "dpi": 300},
-    remove_text=True,
-    style="ggplot",
-    tolerance=20,
-)
-def test_plot():
-    ts = traces.TimeSeries()
-    ts[0] = 0
-    ts[1] = 2
-    ts[3] = 1
-    ts[5] = 0
-
-    figure, axes = ts.plot()
-    return figure
+matplotlib_importable = importlib.util.find_spec("matplotlib")
 
 
-def test_invalid_call():
+def _make_ts():
     ts = traces.TimeSeries()
     ts[0] = 0
     ts[1] = 1
+    return ts
 
-    ts.plot(interpolate="previous")
-    ts.plot(interpolate="linear")
 
-    with pytest.raises(ValueError):
-        ts.plot(interpolate="yomama")
+def test_message_when_matplotlib_not_installed():
+    """When matplotlib is not importable, make sure that calling plot
+    raises an informative error message.
 
+    """
+    if not matplotlib_importable:
+        ts = _make_ts()
 
-def test_empty():
-    ts = traces.TimeSeries()
+        with pytest.raises(ImportError) as error:
+            ts.plot()
 
-    ts.plot()
+        assert "need to install matplotlib" in str(error)

tests/test_plot_external.py

@@ -0,0 +1,38 @@
+import pytest
+
+import traces
+
+
+@pytest.mark.mpl_image_compare(
+    savefig_kwargs={"bbox_inches": "tight", "dpi": 300},
+    remove_text=True,
+    style="ggplot",
+    tolerance=20,
+)
+def test_plot():
+    ts = traces.TimeSeries()
+    ts[0] = 0
+    ts[1] = 2
+    ts[3] = 1
+    ts[5] = 0
+
+    figure, axes = ts.plot()
+    return figure
+
+
+def test_invalid_call():
+    ts = traces.TimeSeries()
+    ts[0] = 0
+    ts[1] = 1
+
+    ts.plot(interpolate="previous")
+    ts.plot(interpolate="linear")
+
+    with pytest.raises(ValueError):
+        ts.plot(interpolate="yomama")
+
+
+def test_empty():
+    ts = traces.TimeSeries()
+
+    ts.plot()