Refactor rdrgen tests

tests/test_rdrgen.py

-from datetime import datetime
 import os
 import subprocess
 from StringIO import StringIO
+from datetime import datetime
 
 import h5py
 
@@ -9,30 +9,9 @@ import edosl0util.rdrgen as m
 from edosl0util.jpssrdr import decode_rdr_blob
 from edosl0util.stream import jpss_packet_stream
 
-snpp_base_time = 1698019234000000  # from CDFCB vol I "Time of First Ascending Node" table
-cris_gran_len = 31997000
-
-
-def test_calc_iet_granule():
-    run = lambda t: m.calc_iet_granule(snpp_base_time, cris_gran_len, t)
-    gran = 1880240293174000
-    prev_gran = 1880240261177000
-    next_gran = 1880240325171000
-    assert run(gran) == gran
-    assert run(gran + 1) == gran
-    assert run(gran - 1) == prev_gran
-    assert run(gran + cris_gran_len) == next_gran
-
 
-def test_calc_iet_aggregate():
-    grans_per_aggr = 15
-    run = lambda t: m.calc_iet_aggregate(snpp_base_time, cris_gran_len, grans_per_aggr, t)
-    aggr = 1880240037198000
-    aggr_len = grans_per_aggr * cris_gran_len
-    assert run(aggr - 1) == aggr - aggr_len
-    assert run(aggr) == aggr
-    assert run(aggr + aggr_len - 1) == aggr
-    assert run(aggr + aggr_len) == aggr + aggr_len
+class TestViirsGroupedPacketTimeTracker(object):
+    pass
 
 
 def test_can_reproduce_rdr_from_class():
@@ -68,3 +47,31 @@ def test_can_reproduce_rdr_from_class():
         stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
     assert p.communicate()[0] == ''
     assert p.returncode == 0
+
+
+class TestGranulation(object):
+    def test_calc_iet_granule(self):
+        def run(t):
+            return m.calc_iet_granule(self.snpp_base_time, self.cris_gran_len, t)
+        gran = 1880240293174000
+        prev_gran = 1880240261177000
+        next_gran = 1880240325171000
+        assert run(gran) == gran
+        assert run(gran + 1) == gran
+        assert run(gran - 1) == prev_gran
+        assert run(gran + self.cris_gran_len) == next_gran
+
+    def test_calc_iet_aggregate(self):
+        grans_per_aggr = 15
+        def run(t):
+            return m.calc_iet_aggregate(
+                self.snpp_base_time, self.cris_gran_len, grans_per_aggr, t)
+        aggr = 1880240037198000
+        aggr_len = grans_per_aggr * self.cris_gran_len
+        assert run(aggr - 1) == aggr - aggr_len
+        assert run(aggr) == aggr
+        assert run(aggr + aggr_len - 1) == aggr
+        assert run(aggr + aggr_len) == aggr + aggr_len
+
+    snpp_base_time = 1698019234000000  # CDFCB vol I "Time of First Ascending Node" table
+    cris_gran_len = 31997000