Updating Values on json file A using reference on file B - The return - awk

Question

Ok, i should feel ashamed for that, but i'm unable to understand how awk works...
A few days ago i posted this question which questions about how to replace fields on file A using the file B as a reference ( both files have matching ID's for reference ).
But after accepting the answer as correct ( Thanks Ed !) i'm struggling about how to do it using this following pattern:
File A
{"test_ref":32132112321,"test_id":12345,"test_name":"","test_comm":"test", "null_test": "true"}
{"test_ref":32133321321,"test_id":12346,"test_name":"","test_comm":"test", "test_type": "alfa"}
{"test_ref":32132331321,"test_id":12347,"test_name":"","test_comm":"test", "test_val": 1923}
File B
{"test_id": 12345, "test_name": "Test values for null"}
{"test_id": 12346, "test_name": "alfa tests initiated"}
{"test_id": 12347, "test_name": "discard values"}
Expected result:
{"test_ref":32132112321,"test_id":12345,"test_name":"Test values for null","test_comm":"test", "null_test": "true"}
{"test_ref":32133321321,"test_id":12346,"test_name":"alfa tests initiated","test_comm":"test", "test_type": "alfa"}
{"test_ref":32132331321,"test_id":12347,"test_name":"discard values","test_comm":"test", "test_val": 1923}
I tried some alterations with the original solution but without success. So, Based on the Question posted before, how could i achieve the same results with this new pattern?
PS: One important note, the lines on file A not always have the same length
Big Thanks in advance.
EDIT:
After trying the solution posted by Wintermute, it seens it doens't work with lines having:
{"test_ref":32132112321,"test_id":12345,"test_name":"","test_comm":"test", "null_test": "true","modifiers":[{"type":3,"value":31}{"type":4,"value":33}]}
Error received.
error: parse error: Expected separator between values at line xxx, column xxx

Answer 1

Parsing JSON with awk or sed is not a good idea for the same reasons that it's not a good idea to parse XML with them: sed works based on lines, and JSON is not line-based. awk works on vaguely tabular data, and JSON is not vaguely tabular. People don't expect their JSON tools to break when they insert newlines in benign places.
Instead, consider using a tool geared towards JSON processing, such as jq. In this particular case, you could use
jq -c -s 'group_by(.test_id) | map(.[0] + .[1]) | .[]' a.json b.json > c.json
Here jq slurps (-s) the input files into an array of JSON objects, groups these by test_id, merges them and unpacks the array. -c means compact output format, so each JSON object in the result ends up on a single line in the output.