test(find): add find function tests

src/__tests__/find.spec.ts

@@ -0,0 +1,56 @@
+import find from '../find';
+
+describe('find', () => {
+  test('should return the first key which matches the callback evaluation', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+      c: 3,
+    };
+
+    expect(find(obj, (k, v) => k === 'a' && v === 1)).toBe('a');
+    expect(find(obj, (k, v) => k === 'b' && v === 2)).toBe('b');
+    expect(find(obj, (k, v) => k === 'c' && v === 3)).toBe('c');
+  });
+
+  test('should the key of a deep object when follow is true', () => {
+    const obj = {
+      a: 1,
+      b: {
+        c: 2,
+        d: {
+          e: 3,
+        },
+      },
+    };
+
+    expect(find(obj, (k, v) => k === 'b.c' && v === 2, {
+      follow: true,
+    })).toBe('b.c');
+    expect(find(obj, (k, v) => k === 'b.d.e' && v === 3, {
+      follow: true,
+    })).toBe('b.d.e');
+  });
+
+  test('if all callbacks evaluate to false return undefined', () => {
+    expect(find({}, () => false)).toBe(undefined);
+    expect(find({}, () => false, {
+      follow: true,
+    })).toBe(undefined);
+  });
+
+  test('should throw TypeError for invalid arguments', () => {
+    const invalidObj: unknown = 'testing';
+    const invalidCallback: unknown = 'testing';
+    const invalidFollow: unknown = 'testing';
+
+    expect(() => find(invalidObj as OObject, jest.fn()))
+      .toThrow(new TypeError('Expected Object, got string testing'));
+    expect(() => find({}, invalidCallback as FindCallback))
+      .toThrow(new TypeError('Expected Function, got string testing'));
+    expect(() => find({}, jest.fn(), {
+      follow: invalidFollow as boolean,
+    }))
+      .toThrow(new TypeError('Expected Boolean, got string testing'));
+  });
+});