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Test Sub-Pattern

Prerequisite Check

Before writing tests, verify the pattern has:

• pattern<Input, Output>() (not single-type pattern<State>())
• Actions typed as Stream<T> in Output interface
• Bound handlers returned from the pattern

If missing, fix the pattern first – tests can’t call .send() without proper Output types.

Read First

• docs/common/workflows/pattern-testing.md – Full test file format and prerequisites

Test Command

deno task ct test packages/patterns/[name]/[file].test.tsx

Test File Template

import { action, computed, pattern } from "commontools";
import Pattern from "./pattern.tsx";

export default pattern(() => {
  // 1. Instantiate pattern under test
  const instance = Pattern({ /* input */ });

  // 2. Define actions (trigger events)
  const action_do_something = action(() => {
    instance.someAction.send();
  });

  // 3. Define assertions (computed booleans)
  const assert_initial_state = computed(() => instance.someField === expectedValue);
  const assert_after_action = computed(() => instance.someField === newValue);

  // 4. Return tests array
  return {
    tests: [
      { assertion: assert_initial_state },
      { action: action_do_something },
      { assertion: assert_after_action },
    ],
  };
});

Key Points

• Test each sub-pattern BEFORE writing the next one
• Use .send() to trigger actions (requires Stream in Output type)
• Use direct property access to read values (not .get())
• Use computed(() => boolean) for assertions

Done When

• Test file exists alongside pattern
• Tests pass
• Ready for next sub-pattern