Added test suite based on nosetests. Closes #27.

tests/test_plot_background/geometry.xml

@@ -0,0 +1,8 @@
+<?xml version="1.0"?>
+<geometry>
+
+  <!-- Sphere with radius 10 -->
+  <surface id="1" type="sphere" coeffs="0 0 0 10" boundary="vacuum"/>
+  <cell id="1" material="1" surfaces="-1" />
+    
+</geometry>

tests/test_plot_background/materials.xml

@@ -0,0 +1,9 @@
+<?xml version="1.0"?>
+<materials>
+
+  <material id="1">
+    <density value="4.5" units="g/cc" />
+    <nuclide name="U-235" xs="70c" ao="1.0" />
+  </material>
+
+</materials>

tests/test_plot_background/plots.xml

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+<?xml version="1.0"?>
+<plots>
+
+  <plot id="1">
+    <origin>0. 0. 0.</origin>
+    <width>30. 30.</width>
+    <pixels>200 200</pixels>
+    <background>0 0 0</background>
+  </plot>
+
+</plots>

tests/test_plot_background/settings.xml

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+<?xml version="1.0"?>
+<settings>
+
+  <eigenvalue>
+    <batches>10</batches>
+    <inactive>5</inactive>
+    <particles>1000</particles>
+  </eigenvalue>
+
+  <source>
+    <space type="box">
+      <parameters>-4 -4 -4  4  4  4</parameters>
+    </space>
+  </source>
+
+</settings>

tests/test_plot_background/test_plot_background.py

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+#!/usr/bin/env python
+
+import os
+from subprocess import Popen, STDOUT, PIPE
+
+pwd = os.path.dirname(__file__)
+
+def setup(): 
+    os.putenv('PWD', pwd)
+    os.chdir(pwd)
+
+def test_run():
+    proc = Popen([pwd + '/../../src/openmc', '-p'], stderr=STDOUT, stdout=PIPE)
+    returncode = proc.wait()
+    print(proc.communicate()[0])
+    assert returncode == 0
+
+def test_plot_exists():
+    assert os.path.exists(pwd + '/1_plot.ppm')
+
+def teardown():
+    output = [pwd + '/1_plot.ppm']
+    for f in output:
+        if os.path.exists(f):
+            os.remove(f)