Enable escape and once tests (#4618)

test/once.test.js

@@ -0,0 +1,36 @@
+import assert from 'assert';
+import { _ } from './utils.js';
+
+describe('once', function() {
+  it('should invoke `func` once', function() {
+    var count = 0,
+        once = _.once(function() { return ++count; });
+
+    once();
+    assert.strictEqual(once(), 1);
+    assert.strictEqual(count, 1);
+  });
+
+  it('should ignore recursive calls', function() {
+    var count = 0;
+
+    var once = _.once(function() {
+      once();
+      return ++count;
+    });
+
+    assert.strictEqual(once(), 1);
+    assert.strictEqual(count, 1);
+  });
+
+  it('should not throw more than once', function() {
+    var once = _.once(function() {
+      throw new Error;
+    });
+
+    assert.throws(once);
+
+    once();
+    assert.ok(true);
+  });
+});