Add tests for math/average

Author: przemyslawzalewski

math/average.test.ts

@@ -3,7 +3,20 @@
 import average from "./average.ts";
 
 describe("average", () => {
-  it.skip("TODO", () => {
-    expect(average()).toBeDefined();
+  it("returns average for the given data", () => {
+    expect(average([1, 11, 54, 13, 93, 54, 7, 30, 96, 15])).toBe(374 / 10);
+  });
+
+  it("returns the element itself for single element arrays", () => {
+    expect(average([93])).toBe(93);
+  });
+
+  it("returns 0 for empty arrays", () => {
+    expect(average([])).toBe(0);
+  });
+
+  it("returns 0 for falsy argument", () => {
+    expect(average(null)).toBe(0);
+    expect(average(undefined)).toBe(0);
   });
 });