TST: Simplify test_examples and convert to unittest TestCase

Also, remove use of os.chdir() in the test, which causes other tests
to break by changing the current directory in the middle of the test
run.

tests/test_examples.py

@@ -18,46 +18,25 @@
 
 # Disable plotting
 #
-import matplotlib
 
-import os
-from os import path
-
-try:
-    from path import walk
-except ImportError:
-    # Assume Python 3
-    from os import walk
-
-import fnmatch
+import glob
 import imp
+import matplotlib
+from nose_parameterized import parameterized
+import os
+from unittest import TestCase
 
 matplotlib.use('Agg')
 
 
-def test_examples():
-    os.chdir(example_dir())
-    for fname in all_matching_files(example_dir(), '*.py'):
-        yield check_example, fname
-
-
-def all_matching_files(d, pattern):
-    def addfiles(fls, dir, nfiles):
-        nfiles = fnmatch.filter(nfiles, pattern)
-        nfiles = [path.join(dir, f) for f in nfiles]
-        fls.extend(nfiles)
-
-    files = []
-    for dirpath, dirnames, filenames in walk(d):
-        addfiles(files, dirpath, filenames)
-    return files
-
-
 def example_dir():
     import zipline
-    d = path.dirname(zipline.__file__)
-    return path.join(path.abspath(d), 'examples/')
+    d = os.path.dirname(zipline.__file__)
+    return os.path.join(os.path.abspath(d), 'examples')
 
 
-def check_example(p):
-    imp.load_source('__main__', path.basename(p))
+class ExamplesTests(TestCase):
+    @parameterized.expand(((os.path.basename(f).replace('.', '_'), f) for f in
+                           glob.glob(os.path.join(example_dir(), '*.py'))))
+    def test_example(self, name, example):
+        imp.load_source('__main__', os.path.basename(example), open(example))