MergingDataSpec:
Data
- should be merged
  + Given a table with 20 rows 
  + When we use 'replaceWhere' to write 20 new rows that have partition keys {0} and where the merge condition is 'partitionKey = 0' 
  + And the distribution of partition keys to row counts looks like:
Partition Key  Count          
-------------  -----          
0              4
1              4
2              4
3              4
4              4 
  + Then the partition IDs that are not 0 will not change but partition 0 will have the new rows 
  + And the distribution of partition keys to row counts looks like:
Partition Key  Count          
-------------  -----          
0              20
1              4
2              4
3              4
4              4
where the data with partition key '0' has been upserted 
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +  
- should not be merged if the partition key is not defined
  + Given a table with partition keys 0, 1, 2, 3, 4 
  + When we use 'replaceWhere' to write 20 new rows that have partition keys {0, 1, 2, 3, 4} and where the merge condition is 'partitionKey = 0' 
  + Then a DeltaInvariantViolationException$ is thrown 
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +  
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +