Support arrays in t.like() assertion

docs/03-assertions.md

@@ -141,9 +141,9 @@ Assert that `actual` is not deeply equal to `expected`. The inverse of `.deepEqu
 
 Assert that `actual` is like `selector`. This is a variant of `.deepEqual()`, however `selector` does not need to have the same enumerable properties as `actual` does.
 
-Instead AVA derives a *comparable* object from `actual`, based on the deeply-nested properties of `selector`. This object is then compared to `selector` using `.deepEqual()`.
+Instead AVA derives a *comparable* value from `actual`, recursively based on the shape of `selector`. This value is then compared to `selector` using `.deepEqual()`.
 
-Any values in `selector` that are not regular objects should be deeply equal to the corresponding values in `actual`.
+Any values in `selector` that are not arrays or regular objects should be deeply equal to the corresponding values in `actual`.
 
 In the following example, the `map` property of `actual` must be deeply equal to that of `selector`. However `nested.qux` is ignored, because it's not in `selector`.
 
@@ -162,6 +162,12 @@ t.like({
 })
 ```
 
+You can also use arrays, but note that any indices in `actual` that are not in `selector` are ignored:
+
+```js
+t.like([1, 2, 3], [1, 2])
+```
+
 Finally, this returns a boolean indicating whether the assertion passed.
 
 ### `.throws(fn, expectation?, message?)`
@@ -172,7 +178,7 @@ Assert that an error is thrown. `fn` must be a function which should throw. The
 
 * `instanceOf`: a constructor, the thrown error must be an instance of
 * `is`: the thrown error must be strictly equal to `expectation.is`
-* `message`: the following types are valid: 
+* `message`: the following types are valid:
   * *string* - it is compared against the thrown error's message
   * *regular expression* - it is matched against this message
   * *function* - it is passed the thrown error message and must return a boolean for whether the assertion passed
@@ -207,7 +213,7 @@ The thrown value *must* be an error. It is returned so you can run more assertio
 
 * `instanceOf`: a constructor, the thrown error must be an instance of
 * `is`: the thrown error must be strictly equal to `expectation.is`
-* `message`: the following types are valid: 
+* `message`: the following types are valid:
   * *string* - it is compared against the thrown error's message
   * *regular expression* - it is matched against this message
   * *function* - it is passed the thrown error message and must return a boolean for whether the assertion passed

lib/like-selector.js

@@ -1,8 +1,12 @@
+const isObject = selector => Reflect.getPrototypeOf(selector) === Object.prototype;
+
 export function isLikeSelector(selector) {
-	return selector !== null
-		&& typeof selector === 'object'
-		&& Reflect.getPrototypeOf(selector) === Object.prototype
-		&& Reflect.ownKeys(selector).length > 0;
+	if (selector === null || typeof selector !== 'object') {
+		return false;
+	}
+
+	const keyCount = Reflect.ownKeys(selector).length;
+	return (Array.isArray(selector) && keyCount > 1) || (isObject(selector) && keyCount > 0);
 }
 
 export const CIRCULAR_SELECTOR = new Error('Encountered a circular selector');
@@ -18,7 +22,7 @@ export function selectComparable(lhs, selector, circular = new Set()) {
 		return lhs;
 	}
 
-	const comparable = {};
+	const comparable = Array.isArray(selector) ? [] : {};
 	for (const [key, rhs] of Object.entries(selector)) {
 		if (isLikeSelector(rhs)) {
 			comparable[key] = selectComparable(Reflect.get(lhs, key), rhs, circular);

test-tap/assert.js

@@ -761,6 +761,16 @@ test('.like()', t => {
 		values: [{label: 'Difference (- actual, + expected):', formatted: /{\n-\s*a: 'foo',\n\+\s*a: 'bar',\n\s*}/}],
 	});
 
+	passes(t, () => assertions.like({a: [{a: 1, b: 2}]}, {a: [{a: 1}]}));
+	passes(t, () => assertions.like([{a: 1, b: 2}], [{a: 1}]));
+	passes(t, () => assertions.like([{a: 1, b: 2}, {c: 3}], [{a: 1}]));
+
+	passes(t, () => assertions.like([1, 2, 3], [1, 2, 3]));
+	passes(t, () => assertions.like([1, 2, 3], [1, 2]));
+
+	fails(t, () => assertions.like([1, 2, 3], [3, 2, 1]));
+	fails(t, () => assertions.like([1, 2], [1, 2, 3]));
+
 	t.end();
 });