test(slice): add slice function tests

src/__tests__/slice.spec.ts

@@ -0,0 +1,91 @@
+import slice from '../slice';
+
+describe('slice', () => {
+  test('should return a new object not a reference', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+    };
+
+    const result = slice(obj, 0, 0);
+    result.a = 2;
+
+    expect(typeof result).toBe('object');
+    expect(obj.a).toBe(1);
+  });
+
+  test('should only return the object keys within the slice range', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+      c: 3,
+      d: 4,
+      e: 5,
+    };
+
+    const resultA = slice(obj, 0, 1);
+    const resultB = slice(obj, 2, 4);
+
+    expect(Object.keys(resultA)).toHaveLength(1);
+    expect(Object.keys(resultA)[0]).toBe('a');
+    expect(Object.keys(resultB)).toHaveLength(2);
+    expect(Object.keys(resultB)[0]).toBe('c');
+    expect(Object.keys(resultB)[1]).toBe('d');
+  });
+
+  test('should slice deep objects when follow is true', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+      c: {
+        d: 4,
+        e: 5,
+      },
+    };
+
+    const resultA = slice(obj, 0, 1, {
+      follow: true,
+    });
+    const resultB = slice(obj, 2, 3, {
+      follow: true,
+    });
+
+    expect(Object.keys(resultA)).toHaveLength(1);
+    expect(Object.keys(resultA)[0]).toBe('a');
+    expect(Object.keys(resultB)).toHaveLength(1);
+    expect(Object.keys(resultB)[0]).toBe('c');
+    expect(Object.keys(resultB.c)).toHaveLength(1);
+    expect(Object.keys(resultB.c)[0]).toBe('d');
+  });
+
+  test('end argument should default to object key length', () => {
+    const obj = {
+      a: 1,
+      b: 2,
+      c: 3,
+    };
+
+    const result = slice(obj, 1);
+
+    expect(Object.keys(result)).toHaveLength(2);
+    expect(Object.keys(result)[0]).toBe('b');
+    expect(Object.keys(result)[1]).toBe('c');
+  });
+
+  test('should throw TypeError for invalid arguments', () => {
+    const invalidObj: unknown = 'testing';
+    const invalidNumber: unknown = 'testing';
+    const invalidFollow: unknown = 'testing';
+
+    expect(() => slice(invalidObj as OObject, 0, 0))
+      .toThrow(new TypeError('Expected Object, got string testing'));
+    expect(() => slice({}, invalidNumber as number, 0))
+      .toThrow(new TypeError('Expected Number, got string testing'));
+    expect(() => slice({}, 0, invalidNumber as number))
+      .toThrow(new TypeError('Expected Number, got string testing'));
+    expect(() => slice({}, 0, 0, {
+      follow: invalidFollow as boolean,
+    }))
+      .toThrow(new TypeError('Expected Boolean, got string testing'));
+  });
+});