added download test, added travis tests for different python versions

.travis.yml

@@ -4,7 +4,9 @@ notifications:
   email: false
 python:
   # We don't actually use the Travis Python, but this keeps it organized.
-  - "3.6"
+  - "2.7"
+  - "3.4"
+  - "3.7"
 install:
   # You may want to periodically update this, although the conda update
   # conda line below will keep everything up-to-date.  We do this

tests/test_download.py

@@ -7,6 +7,7 @@
 from merra.download import get_last_folder
 from merra.download import get_first_folder
 from merra.download import folder_get_version_first_last
+from merra.download import get_start_date
 
 
 class Test(unittest.TestCase):
@@ -76,7 +77,10 @@ def test_get_start_end(self):
         assert version == version_should
         assert end == end_should
         assert start == start_should
-
+
+    def test_get_start_date(self):
+        product = 'M2T1NXLND.5.12.4'
+        assert get_start_date(product) == datetime(1980, 1, 1)
 
 if __name__ == "__main__":
     unittest.main()