Validate that start date precedes end date

CHANGELOG.md

@@ -3,6 +3,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
+## [Unreleased]
+### Fixed
+- Raise a clear error when --start-date is later than --end-date instead of an opaque HTTP 400 from CMR [145](https://github.com/podaac/data-subscriber/issues/145)
+
 ## [1.15.2]
 ### Fixed
 - Fixed bug where --subset in combination with the subscriber caused errors

subscriber/podaac_access.py

@@ -192,20 +192,27 @@ def validate(args):
             raise ValueError('Error parsing "--bounds": S Latitude must be <= N Latitude')
 
 
+    start = None
+    end = None
+
     if args.startDate:
         try:
-            datetime.strptime(args.startDate, '%Y-%m-%dT%H:%M:%SZ')
+            start = datetime.strptime(args.startDate, '%Y-%m-%dT%H:%M:%SZ')
         except ValueError:
             raise ValueError(
                 "Error parsing '--start-date' date: " + args.startDate + ". Format must be like 2021-01-14T00:00:00Z")  # noqa E501
 
     if args.endDate:
         try:
-            datetime.strptime(args.endDate, '%Y-%m-%dT%H:%M:%SZ')
+            end = datetime.strptime(args.endDate, '%Y-%m-%dT%H:%M:%SZ')
         except ValueError:
             raise ValueError(
                 "Error parsing '--end-date' date: " + args.endDate + ". Format must be like 2021-01-14T00:00:00Z")  # noqa E501
 
+    if start is not None and end is not None and start > end:
+        raise ValueError(
+            "--end-date must be greater than or equal to --start-date.")
+
     if 'minutes' in args:
         if args.minutes:
             try:

tests/test_subscriber.py

@@ -146,6 +146,13 @@ def test_validate():
     assert a.endDate == '2021-01-01T00:00:00Z'
     assert a.provider == "POCLOUD"
 
+    # start date equal to end date is allowed
+    validate(["-c", "dataset", "-d", "/data", "-sd", "2021-01-01T00:00:00Z", "-ed", "2021-01-01T00:00:00Z"])
+
+    # start date after end date should raise a clear error
+    with pytest.raises(ValueError):
+        validate(["-c", "dataset", "-d", "/data", "-sd", "2021-01-01T00:00:00Z", "-ed", "2020-01-01T00:00:00Z"])
+
     a = validate(["-c", "dataset", "-d", "/data", "-p", "ANEWCLOUD"])
     assert a.provider == 'ANEWCLOUD'