feat: Add axe.utils.assert method

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)
+  }
+}

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)
+    }
+  })
+})