Inside the jstest remove_shard_util.js (line 7) we are asserting that a command will work (removing a shard) and then handle the output error situation of that call. So, when the removeShard fails, we will get a failure on the test.
 

 let res = assert.commandWorked(st.s.adminCommand({removeShard: shardName}));
 if (!res.ok && res.code === ErrorCodes.ShardNotFound) {
     // ...
    return true;
 }

 
We should get the result on the variable first and then handle the error before asserting that the command worked.