Why does Mountebank predicate cause 200 instead of 500 in response? - predicate

Question

Teaching self mountebank. I want to create a mock endpoint such that by issuing POST command to http://localhost:2525/test?mock-response-code=500, the response code will be 500 and the message body will be some custom text.
When I create the imposter, however, and run the relevant curl command, I am getting a 200 response.
curl -i -X POST http://localhost:2525/imposters --data '#createImposter_r500.ejs'
info: [mb:2525] POST /imposters
info: [http:61161] Open for business...
HTTP/1.1 201 Created
Access-Control-Allow-Origin: *
Location: http://localhost:2525/imposters/61161
Content-Type: application/json; charset=utf-8
Content-Length: 767
Date: Sun, 18 Aug 2019 13:57:57 GMT
Connection: keep-alive
{
"protocol": "http",
"port": 61161,
"numberOfRequests": 0,
"recordRequests": false,
"requests": [],
"stubs": [
{
"responses": [
{
"is": {
"statusCode": 500
}
}
],
"predicates": [
{
"equals": {
"path": "/test",
"method": "POST",
"query": {
"mock-response-code": 500
}
}
}
],
"_links": {
"self": {
"href": "http://localhost:2525/imposters/61161/stubs/0"
}
}
}
],
"_links": {
"self": {
"href": "http://localhost:2525/imposters/61161"
},
"stubs": {
"href": "http://localhost:2525/imposters/61161/stubs"
}
}
}
createImposter_r500.ejs:
{
"protocol": "http",
"stubs": [{
"responses": [
{ "is": { "statusCode": 500 }}
],
"predicates": [{
"equals": {
"path": "/test",
"method": "POST",
"query": {"mock-response-code": 500}
}
}]
}]
}
Here is what happens when I try using that URL:
curl -i -X POST http://localhost:61161/test?mock-response-code=500
info: [http:61161] ::1:61429 => POST /test?mock-response-code=500
HTTP/1.1 200 OK
Connection: close
Date: Sun, 18 Aug 2019 14:18:06 GMT
Transfer-Encoding: chunked
Here is some debug output:
debug: [http:62650] ::1:63139 ESTABLISHED
info: [http:62650] ::1:63139 => POST /test?mock-response-code=400
debug: [http:62650] ::1:63139 => {"requestFrom":"::1:63139","method":"POST","path":"/test","query":{"mock-response-code":"400"},"headers":{"Host":"localhost:62650","User-Agent":"curl/7.54.0","Accept":"*/*"},"body":"","ip":"::1"}
debug: [http:62650] no predicate match
debug: [http:62650] generating response from {"is":{}}
debug: [http:62650] ::1:63139 <= {"statusCode":200,"headers":{"Connection":"close"},"body":"","_mode":"text"}
debug: [http:62650] ::1:63139 CLOSED
(Port is different from above b/c it's from a different run.)

Answer 1

I found the answer myself with continued experimentation.
Quotation marks - that simple.
"query": {"mock-response-code": "400"}
rather than
"query": {"mock-response-code": 400}