- split test_axis.py in test_axis.py and test_axiscollection.py

- updated unittests in test_session.py, test_axis.py, test_axiscollection.py and test_group.py --> changed syntax: nosetest --> pytest

Author: alixdamman

larray/tests/common.py

@@ -98,3 +98,7 @@ def nan_equal(a, b):
 
 assert_nparray_equiv = assert_nparray_equal_factory(equal)
 assert_nparray_nan_equiv = assert_nparray_equal_factory(nan_equal)
+
+
+def assert_axis_eq(axis1, axis2):
+    assert axis1.equals(axis2)