From 2f10d24ecdb617e232d51078657082867c4c423d Mon Sep 17 00:00:00 2001
From: Wilco Fiers <wilco.fiers@deque.com>
Date: Fri, 30 Aug 2019 12:47:51 +0200
Subject: [PATCH] feat: Add axe.utils.assert method

---
 lib/core/utils/assert.js  | 12 ++++++++++++
 test/core/utils/assert.js | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 48 insertions(+)
 create mode 100644 lib/core/utils/assert.js
 create mode 100644 test/core/utils/assert.js

diff --git a/lib/core/utils/assert.js b/lib/core/utils/assert.js
new file mode 100644
index 0000000000..a6663ccf7c
--- /dev/null
+++ b/lib/core/utils/assert.js
@@ -0,0 +1,12 @@
+/* global axe*/
+
+/**
+ * If the first argument is falsey, throw an error using the second argument as a message.
+ * @param {boolean} bool
+ * @param {string} message
+ */
+axe.utils.assert = function assert (bool, message) {
+  if (!bool) {
+    throw new Error(message)
+  }
+}
diff --git a/test/core/utils/assert.js b/test/core/utils/assert.js
new file mode 100644
index 0000000000..0aad56f635
--- /dev/null
+++ b/test/core/utils/assert.js
@@ -0,0 +1,36 @@
+describe('axe.utils.assert', function () {
+  it('does nothing when passed a truthy value', function () {
+    assert.doesNotThrow(function () {
+      axe.utils.assert(true)
+      axe.utils.assert('foo')
+      axe.utils.assert(123)
+      axe.utils.assert([])
+      axe.utils.assert({})
+    })
+  })
+
+  it('throws an error when passed a falsey value', function () {
+    assert.throws(function () {
+      axe.utils.assert(false)
+    })
+    assert.throws(function () {
+      axe.utils.assert(0)
+    })
+    assert.throws(function () {
+      axe.utils.assert(null)
+    })
+    assert.throws(function () {
+      axe.utils.assert(undefined)
+    })
+  })
+
+  it('sets second argument as the error message', function () {
+    var message = 'Something went wrong'
+    try {
+      axe.utils.assert(false, message)
+    } catch (e) {
+      assert.instanceOf(e, Error)
+      assert.equal(e.message, message)
+    }
+  })
+})
\ No newline at end of file