write-canary-tests

name	write-canary-tests
description	Write correct test blocks and assertions for Mission Control canary health checks. Use when creating canaries that need pass/fail conditions, adding test expressions, or writing assertions based on HTTP status, JSON response, exec output, or Kubernetes health.

Write Canary Tests

Goal

Write correct test blocks for canary checks.

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Golden Rules

• The test result must be boolean (true / false).
• Use null-safe access for optional fields (.? + orValue(...)).
• Tests add assertions; they do not bypass built-in check failures.

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Test Fields

Field	Description	Example
expr	CEL expression that evaluates to boolean	code == 200 && json.status == 'ok'
javascript	JavaScript expression/script returning true / false	code === 200
template	Go template rendering true / false	{{ eq .code 200 }}

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Common Test Context

Exact fields vary by check type.

Variable	Description	Example
results	Primary result payload for many check types	size(results) > 0
code	HTTP status code (HTTP checks)	code in [200, 201, 301]
json	Parsed JSON response body (HTTP checks)	json.headers['User-Agent'] != ''
headers	HTTP response headers	'Content-Type' in headers.keys()
sslAge	SSL validity duration (HTTP TLS checks)	sslAge > Duration('7d')
outputs.<checkName>	Previous named check outputs (with dependsOn)	outputs.getUuid.json.uuid != ''
check	Current check metadata	check.name != ''
canary	Current canary metadata	canary.namespace == 'prod'

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Canonical Snippets

1) HTTP status + JSON assertion

test:
  expr: "code == 200 && json.uuid != ''"

2) HTTP header assertion

test:
  expr: "! ('Authorization' in headers.keys())"

3) Exec stdout assertion

test:
  expr: 'results.stdout == "hello"'

4) Kubernetes health assertion

test:
  expr: dyn(results).all(x, k8s.isHealthy(x))

5) JUnit summary assertion

test:
  expr: results.failed == 0 && results.passed > 0

6) dependsOn output assertion

test:
  expr: "code == 200 && outputs.getUuid.json.uuid != ''"

7) Nil-safe list check

test:
  expr: results.?files.orValue([]).size() > 0

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References

• Canary Checker spec reference: https://flanksource.com/docs/reference/canary-checker/llms.txt