Best way for setting Up data for Unit testing

What is the best way of setting up data for unit testing spanning all possible test-cases ? I have different situations where I need to check for null exceptions and other custom exceptions . In order to test such exceptions I have to setup data again & again with some fields changed & some unchanged.Finally, my test method writes to an excel file & I have to assert against each column value (have 50 such columns) with the expected values. Should storing set up data and assertion expected data in json be a good approach here ?