Implement 'from_string_or_404' util and its example usage.

common/djangoapps/util/tests/test_course_key_utils.py

@@ -0,0 +1,32 @@
+"""
+Tests for util.course_key_utils
+"""
+from nose.tools import assert_equals, assert_raises  # pylint: disable=no-name-in-module
+from util.course_key_utils import from_string_or_404
+from opaque_keys.edx.keys import CourseKey
+from django.http import Http404
+
+
+def test_from_string_or_404():
+
+    #testing with split style course keys
+    assert_raises(
+        Http404,
+        from_string_or_404,
+        "/some.invalid.key/course-v1:TTT+CS01+2015_T0"
+    )
+    assert_equals(
+        CourseKey.from_string("course-v1:TTT+CS01+2015_T0"),
+        from_string_or_404("course-v1:TTT+CS01+2015_T0")
+    )
+
+    #testing with mongo style course keys
+    assert_raises(
+        Http404,
+        from_string_or_404,
+        "/some.invalid.key/TTT/CS01/2015_T0"
+    )
+    assert_equals(
+        CourseKey.from_string("TTT/CS01/2015_T0"),
+        from_string_or_404("TTT/CS01/2015_T0")
+    )