Matplotlib tests + helpers methods

* Maplotlib is an important package. It has now its own test checking that a plot can be generated and exported has an image.
* Some helpers methods added to the `Makefile` mainly permitting to clean containers and images
* Improved assertion messages of some tests

scipy-notebook/test/data/matplotlib_1.py

@@ -0,0 +1,24 @@
+# Matplotlit: Create a simple plot example.
+# Refs: https://matplotlib.org/3.1.1/gallery/lines_bars_and_markers/simple_plot.html
+
+# Optional test with [Matplotlib Jupyter Integration](https://github.com/matplotlib/ipympl)
+# %matplotlib widget
+import matplotlib
+import matplotlib.pyplot as plt
+import numpy as np
+import os
+
+# Data for plotting
+t = np.arange(0.0, 2.0, 0.01)
+s = 1 + np.sin(2 * np.pi * t)
+
+fig, ax = plt.subplots()
+ax.plot(t, s)
+
+ax.set(xlabel='time (s)', ylabel='voltage (mV)',
+       title='About as simple as it gets, folks')
+ax.grid()
+# Note that the test can be run headless by checking if an image is produced
+file_path = os.path.join("/tmp", "test.png")
+fig.savefig(file_path)
+print(f"File {file_path} saved")

scipy-notebook/test/test_matplotlib.py

@@ -0,0 +1,35 @@
+# Copyright (c) Jupyter Development Team.
+# Distributed under the terms of the Modified BSD License.
+
+import logging
+
+import pytest
+import os
+
+LOGGER = logging.getLogger(__name__)
+
+
+def test_matplotlib(container):
+    """Test that matplotlib is able to plot a graph and write it as an image"""
+    host_data_dir = os.path.join(os.path.dirname(os.path.realpath(__file__)), "data")
+    cont_data_dir = "/home/jovyan/data"
+    test_file = "matplotlib_1.py"
+    output_dir = "/tmp"
+    LOGGER.info(f"Test that matplotlib is able to plot a graph and write it as an image ...")
+    command = "sleep infinity"
+    running_container = container.run(
+        volumes={host_data_dir: {"bind": cont_data_dir, "mode": "ro"}},
+        tty=True,
+        command=["start.sh", "bash", "-c", command],
+    )
+    command = f"python {cont_data_dir}/{test_file}"
+    cmd = running_container.exec_run(command)
+    assert cmd.exit_code == 0, f"Command {command} failed"
+    LOGGER.debug(cmd.output.decode("utf-8"))
+    # Checking if the file is generated
+    # https://stackoverflow.com/a/15895594/4413446
+    expected_file = f"{output_dir}/test.png"
+    command = f"test -s {expected_file}"
+    cmd = running_container.exec_run(command)
+    assert cmd.exit_code == 0, f"Command {command} failed"
+    LOGGER.debug(cmd.output.decode("utf-8"))

scipy-notebook/test/test_pandas.py

@@ -21,6 +21,6 @@ def test_pandas(container, name, command):
     LOGGER.info(f"Testing pandas: {name} ...")
     c = container.run(tty=True, command=["start.sh", "python", "-c", command])
     rv = c.wait(timeout=30)
-    assert rv == 0 or rv["StatusCode"] == 0
+    assert rv == 0 or rv["StatusCode"] == 0, f"Command {command} failed"
     logs = c.logs(stdout=True).decode("utf-8")
     LOGGER.debug(logs)