✨ Allow assertion functions to return an assertion object

lib/assertion.js

@@ -20,12 +20,14 @@ import Context from './context.js';
  */
 
 /**
- * @param {AssertSubject} assertion
+ * @param {(AssertObject | AssertSubject)} assertion
  * @param {AssertMessage} [failureMessage]
  * @param {AssertMessage} [negatedMessage]
  * @returns {import('./context').ContextGenerator<{ assert?: boolean }>}
  */
 export function* assert(assertion, failureMessage, negatedMessage) {
+  if (typeof assertion === 'object' && Object.getPrototypeOf(assertion) === Object.prototype)
+    ({ assertion, failureMessage = failureMessage, negatedMessage = negatedMessage } = assertion);
   let expected = yield ({ assert }) => assert?.expected;
   let error, pass;
 
@@ -37,6 +39,10 @@ export function* assert(assertion, failureMessage, negatedMessage) {
     pass = false;
   }
 
+  if (typeof pass === 'object' &&
+    Object.getPrototypeOf(pass) === Object.prototype && 'assertion' in pass
+  ) pass = yield assert(pass, failureMessage, negatedMessage);
+
   if (!!pass !== expected) {
     throw (error ?? new Error((expected
       ? (yield failureMessage) || 'Assertion failed'
@@ -68,10 +74,6 @@ export class Assertion {
    * @param {AssertMessage} [negatedMessage]
    */
   constructor(assertion, failureMessage, negatedMessage) {
-    if (typeof assertion === 'object' &&
-        Object.getPrototypeOf(assertion) === Object.prototype)
-      ({ assertion, failureMessage, negatedMessage } = assertion);
-
     Object.defineProperty(this, Assertion.Symbol, {
       // @ts-ignore
       value: () => assert(assertion, failureMessage, negatedMessage),

tests/interactor.test.js

@@ -571,6 +571,23 @@ describe('Assert', () => {
         'Negated message');
     });
 
+    it('accepts an assertion that returns an assertion object', async () => {
+      TestAssert.defineAssertion('test', (expected, msg) => ({
+        assertion: expected === true,
+        failureMessage: `Failure message (${msg})`,
+        negatedMessage: `Negated message (${msg})`
+      }));
+
+      await assert(typeof T.assert.test === 'function',
+        'Expected test to be a function');
+      await assert(T.assert.test(true) instanceof Assertion,
+        'Expected test to return an Interaction instance');
+      await assert.throws(T.assert.test(false, 'foo'),
+        'Failure message (foo)');
+      await assert.throws(T.assert.not.test(true, 'bar'),
+        'Negated message (bar)');
+    });
+
     it('accepts an assertion class', async () => {
       let pass = false;