test:add test for add exercise

js/tests/add_test.js

@@ -0,0 +1,19 @@
+export const tests = []
+const t = (f) => tests.push(f)
+
+
+// add is declared and is a function and take 2 arguments
+t(() => typeof Add === 'function')
+t(() => Add.length === 2)
+
+// add works with positive numbers
+t(() => Add(5, 6) === 11)
+
+// Add works with negative numbers
+t(() => Add(-5, -6) === -11)
+
+// Add works with mixed numbers
+t(() => Add(-5, 6) === 1)
+
+// Add works with zero
+t(() => Add(0, 0) === 0)