Added test cases for invert.js

Author: Eugenie-A

Sprint-2/interpret/invert.test.js

@@ -0,0 +1,34 @@
+const invert = require("./invert.js");
+
+// Given an object
+// When invert is passed this object
+// Then it should swap the keys and values
+test("invert swaps the keys and values of an object", () => {
+  expect(invert({ x: 10, y: 20 })).toEqual({
+    10: "x",
+    20: "y",
+  });
+});
+
+// Given an object with one key value pair
+// When passed to invert
+// Then it should return the swapped pair
+test("invert swaps a single key value pair", () => {
+  expect(invert({ a: 1 })).toEqual({
+    1: "a",
+  });
+});
+
+// Given an empty object
+// When passed to invert
+// Then it should return an empty object
+test("invert on an empty object returns an empty object", () => {
+  expect(invert({})).toEqual({});
+});
+
+// Given an invalid input like an array
+// When passed to invert
+// Then it should throw an error
+test("invert throws an error for invalid input", () => {
+  expect(() => invert([])).toThrow("Input must be an object");
+});