Use a library called 'insta' to better organize those longer correct test outputs in toplevel tests. 'insta' creates `.snap` files as snapshots of the test output, and will automatically do the diff if the output is different. This makes maintaining test cases with larger outputs a lot easier.
Reviewed-on: M-Labs/nac3#42
Co-authored-by: ychenfo <yc@m-labs.hk>
Co-committed-by: ychenfo <yc@m-labs.hk>
