Test migration to jest by hand

Apparently using regular expressions is way easier.

test/when/when.test.js

@@ -0,0 +1,18 @@
+const expect = require('expect');
+const when = require('./when.js');
+
+
+  test('when is a Function', () => {
+  expect(when).toBeInstanceOf(Function);
+});
+
+  const doubleEvenNumbers = when(
+    (x) => x % 2 === 0,
+    (x) => x * 2
+  );
+
+  t.true(doubleEvenNumbers(2) === 4);
+  t.true(doubleEvenNumbers(1) === 1);
+
+  
+