Unit tests for RollingArray

ui/tests/unit/utils/rolling-array-test.js

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+import { isArray } from '@ember/array';
+import { module, test } from 'ember-qunit';
+import RollingArray from 'nomad-ui/utils/classes/rolling-array';
+
+module('Unit | Util | RollingArray');
+
+test('has a maxLength property that gets set in the constructor', function(assert) {
+  const array = RollingArray(10, 'a', 'b', 'c');
+  assert.equal(array.maxLength, 10, 'maxLength is set in the constructor');
+  assert.deepEqual(
+    array,
+    ['a', 'b', 'c'],
+    'additional arguments to the constructor become elements'
+  );
+});
+
+test('push works like Array#push', function(assert) {
+  const array = RollingArray(10);
+  const pushReturn = array.push('a');
+  assert.equal(
+    pushReturn,
+    array.length,
+    'the return value from push is equal to the return value of Array#push'
+  );
+  assert.equal(array[0], 'a', 'the arguments passed to push are appended to the array');
+
+  array.push('b', 'c', 'd');
+  assert.deepEqual(
+    array,
+    ['a', 'b', 'c', 'd'],
+    'the elements already in the array are left in tact and new elements are appended'
+  );
+});
+
+test('when pushing past maxLength, items are removed from the head of the array', function(assert) {
+  const array = RollingArray(3);
+  const pushReturn = array.push(1, 2, 3, 4);
+  assert.deepEqual(
+    array,
+    [2, 3, 4],
+    'The first argument to push is not in the array, but the following three are'
+  );
+  assert.equal(
+    pushReturn,
+    array.length,
+    'The return value of push is still the array length despite more arguments than possible were provided to push'
+  );
+});
+
+test('when splicing past maxLength, items are removed from the head of the array', function(assert) {
+  const array = RollingArray(3, 'a', 'b', 'c');
+
+  array.splice(1, 0, 'z');
+  assert.deepEqual(
+    array,
+    ['z', 'b', 'c'],
+    'The new element is inserted as the second element in the array and the first element is removed due to maxLength restrictions'
+  );
+
+  array.splice(0, 0, 'pickme');
+  assert.deepEqual(
+    array,
+    ['z', 'b', 'c'],
+    'The new element never makes it into the array since it was added at the head of the array and immediately removed'
+  );
+
+  array.splice(0, 1, 'pickme');
+  assert.deepEqual(
+    array,
+    ['pickme', 'b', 'c'],
+    'The new element makes it into the array since the previous element at the head of the array is first removed due to the second argument to splice'
+  );
+});
+
+test('unshift throws instead of prepending elements', function(assert) {
+  const array = RollingArray(5);
+
+  assert.throws(
+    () => {
+      array.unshift(1);
+    },
+    /Cannot unshift/,
+    'unshift is not supported, but is not undefined'
+  );
+});
+
+test('RollingArray is an instance of Array', function(assert) {
+  const array = RollingArray(5);
+  assert.ok(array.constructor === Array, 'The constructor is Array');
+  assert.ok(array instanceof Array, 'The instanceof check is true');
+  assert.ok(isArray(array), 'The ember isArray helper works');
+});