Predicates in Mountebank

Predicates in Mountebank imposter files is a pretty powerful way to configure stubs. It helps us to return different responses based on the request parameters like type, query string , headers, body etc. Let us have some quick look at extracting values from request

Based on Query String

Below is an example of extracting the records based on query string. If the request is like path?customerId=123&customerId=456&email=abc.com Note: This is slightly modified version of code in mbtest.org

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{
  "port": 4547,
  "protocol": "http",
  "stubs": [
    {
      "predicates": [{
        "equals": {
          "query": { "customerId": ["123", "456"] }
        }
      }],
      "responses": [{
        "is": {
          "body": "Customer ID is either 123 or 456"
        }
      }]
    },
    {
      "predicates": [{
        "equals": {
          "query": { 
              "customerId": "123",
              "email" :"abc.com"
               }
        }
      }],
      "responses": [{
        "is": {
          "body": "Customer ID is 123 and email is abc.com"
        }
      }]
    }
  ]
}

Based on Header Content

If input data is shared through values in header, that can be extracted. Below snippet is directly from mbtest.org

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{
  "port": 4545,
  "protocol": "http",
  "stubs": [
    {
      "responses": [{ "is": { "statusCode": 400 } }],
      "predicates": [
        {
          "equals": {
            "method": "POST",
            "path": "/test",
            "query": {
              "first": "1",
              "second": "2"
            },
            "headers": {
              "Accept": "text/plain"
            }
          }
        },
        {
          "equals": { "body": "hello, world" },
          "caseSensitive": true,
          "except": "!$"
        }
      ]
    }
   ]
 }

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