2 files changed, 49 insertions, 0 deletions
diff --git a/date-fns/src/_lib/requiredArgs/index.ts b/date-fns/src/_lib/requiredArgs/index.ts
new file mode 100644
index 0000000..bdbb950
--- /dev/null
+++ b/date-fns/src/_lib/requiredArgs/index.ts
@@ -0,0 +1,12 @@
+export default function requiredArgs(required: number, args: IArguments) {
+  if (args.length < required) {
+    throw new TypeError(
+      required +
+        ' argument' +
+        (required > 1 ? 's' : '') +
+        ' required, but only ' +
+        args.length +
+        ' present'
+    )
+  }
+}
diff --git a/date-fns/src/_lib/requiredArgs/test.js b/date-fns/src/_lib/requiredArgs/test.js
new file mode 100644
index 0000000..a6cbe4a
--- /dev/null
+++ b/date-fns/src/_lib/requiredArgs/test.js
@@ -0,0 +1,37 @@
+// @flow
+/* eslint-env mocha */
+
+import assert from 'power-assert'
+import requiredArgs from '.'
+
+describe('requiredArgs', function () {
+  function wrapperFn(required) {
+    // $ExpectedMistake
+    return function () {
+      requiredArgs(required, arguments)
+    }
+  }
+  const twoArgsRequired = wrapperFn(2)
+
+  describe('with correct number of passed arguments', function () {
+    it('does not throw an error', function () {
+      assert.doesNotThrow(() => twoArgsRequired(1, 2))
+    })
+  })
+
+  describe('with wrong number of arguments', function () {
+    it('throws correct error message', function () {
+      assert.throws(
+        function () {
+          twoArgsRequired(1)
+        },
+        function (err) {
+          return (
+            err instanceof TypeError &&
+            err.message === '2 arguments required, but only 1 present'
+          )
+        }
+      )
+    })
+  })
+})