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Defining Test Outputs in Text Files

Outputs are really useful when running Test Suites. They allow for exporting values from a test so they become available in the Variable Sets of the current Test Suite.

Outputs are Expression Results​

An output exports the result of an Expression and assigns it to a name, so it can be injected into the variable set of a running Test Suite. A selector is needed only if the provided expression refers to a/some span/s attribute or meta attributes.

It can be defined using the following YAML definition:

outputs:
  - name: USER_ID
    selector: span[name = "user creation"]
    value: attr:myapp.users.created_id

The value attribute is an expression and is a very powerful tool.

Examples​

Basic Expression​

You can output basic expressions:

outputs:

- name: ARITHMETIC_RESULT
  value: 1 + 1
  # results in ARITHMETIC_RESULT = 2

- name: INTERPOLATE_STRING
  # assume PRE_EXISTING_VALUE=someValue from env vars
  value: "the value ${var:PRE_EXISTING_VALUE} comes from the env var PRE_EXISTING_VALUE"
  # results in INTERPOLATE_STRING = "the value someValue comes from the env var PRE_EXISTING_VALUE

Extract a Value from a JSON​

Imagine a hypotetical /users/create endpoint that returns the full user object, including the new ID, when the operation is successful.

outputs:
- name: USER_ID
  selector: span[name = "POST /user/create"]
  value: attr:http.response.body | json_path '.id'

Multiple Values​

Using the same hypotethical user creation endpoint, a user creation might result on multiple sql queries, for example:

  • INSERT INTO users ...
  • INSERT INTO permissions...
  • SELECT remaining_users FROM accounts
  • UPDATE accounts SET remaining_users ...

In this case, the service is instrumented so that each query generates a span of type database. You can get a list of SQL operations:

outputs:
- name: SQL_OPS
  selector: span[tracetest.span.type = "database"]
  value: attr:sql.operation
  # result: SQL_OPS = ["INSERT", "INSERT", "SELECT", "UPDATE"]

Since the value is an array, you can also apply filters to it:

outputs:
- name: LAST_SQL_OP
  selector: span[tracetest.span.type = "database"]
  value: attr:sql.operation | get_index 'last'
  # result: LAST_SQL_OP = "INSERT"