jq not replacing json value with parameter

shell variables in jq scripts should be interpolated or passed as arguments via --arg name value:

jq --arg inp1 "$input1" --arg inp2 "$input2" \'map(if .ParameterKey == "Project"     then . + {"ParameterValue" : ($inp1 + "/solution/" + $inp2 + ".result") } else . end)' test.json

The output:

[  {    "ParameterKey": "Project",    "ParameterValue": "test1/solution/test2.result"  }]

In your jq program, you have quoted "$input1/solution/$input2.result", and therefore it is a JSON string literal, whereas you evidently want string interpolation; you also need to distinguish between the shell variables ($input1 and $input2) on the one hand, and the corresponding jq dollar-variables (which may or may not have the same name) on the other.

Since your shell variables are strings, you could pass them in using the --arg command-line option (e.g. --arg input1 "$input1" if you chose to name the variables in the same way).

You can read up on string interpolation in the jq manual (see https://stedolan.github.io/jq/manual, but note the links at the top for different versions of jq).

There are other ways to achieve the desired results too, but using string interpolation with same-named variables, you'd write:

"\($input1)/solution/\($input2).result" 

Notice that the above string is NOT itself literally a JSON string. Only after string interpolation does it become so.