Add tests and typings for array/are

Author: przemyslawzalewski

array/are.test.ts

@@ -3,7 +3,13 @@
 import are from "./are.ts";
 
 describe("are", () => {
-  it("TODO", () => {
-    expect(are()).toBeDefined();
+  it("returns true if the given arguments are all arrays", () => {
+    expect(are([2, 3])).toBe(true);
+    expect(are([1, 2, 3], [])).toBe(true);
+    expect(are([1, 2, 3], 8, [1, 3], "test")).toBe(false);
+  });
+
+  it("returns true for empty list of arguments", () => {
+    expect(are()).toBe(true);
   });
 });

array/are.ts

@@ -1,3 +1,3 @@
 import is from "./is";
 
-export default (...xs) => xs.every(is);
+export default (...xs: any[]): boolean => xs.every(is);