diff --git a/src/__tests__/defaults.spec.ts b/src/__tests__/defaults.spec.ts
new file mode 100644
index 00000000..ff90363a
--- /dev/null
+++ b/src/__tests__/defaults.spec.ts
@@ -0,0 +1,27 @@
+import defaults from '../defaults'
+import { OObject } from '../types'
+
+describe('defaults', (): void => {
+  test('should merge all objects', (): void => {
+    const getDefaults = defaults({ a: 1 })
+    const b = { b: 2 }
+    const c = { c: 3 }
+    const keys = Object.keys(getDefaults(b, c))
+
+    expect(keys).toHaveLength(3)
+  })
+
+  test('should deep merge objects', (): void => {
+    const getDefaults = defaults({ a: 1, b: { c: 2 } })
+    const b = { b: { c: 3 } }
+
+    expect(getDefaults(b).b.c).toBe(3)
+  })
+
+  test('should throw TypeError if follow argument is invalid', (): void => {
+    const invalidObj: unknown = 'testing'
+
+    expect((): OObject => defaults(invalidObj as OObject))
+      .toThrow(new TypeError('Expected Object, got string testing'))
+  })
+})
diff --git a/src/__tests__/shallowDefaults.spec.ts b/src/__tests__/shallowDefaults.spec.ts
new file mode 100644
index 00000000..a8fe1519
--- /dev/null
+++ b/src/__tests__/shallowDefaults.spec.ts
@@ -0,0 +1,30 @@
+import shallowDefaults from '../shallowDefaults'
+import { OObject } from '../types'
+
+describe('defaults', (): void => {
+  test('should merge all objects', (): void => {
+    const getDefaults = shallowDefaults({ a: 1 })
+    const b = { b: 2 }
+    const c = { c: 3 }
+    const keys = Object.keys(getDefaults(b, c))
+
+    expect(keys).toHaveLength(3)
+  })
+
+  test('should shallow merge objects', (): void => {
+    const getDefaults = shallowDefaults({ a: 1, b: { c: 2, d: 3 } })
+    const b = { a: 2, b: { c: 3 } }
+    const result = getDefaults(b)
+
+    expect(result.a).toBe(2)
+    expect(result.b.c).toBe(3)
+    expect(result.b.d).toBeUndefined()
+  })
+
+  test('should throw TypeError if follow argument is invalid', (): void => {
+    const invalidObj: unknown = 'testing'
+
+    expect((): OObject => shallowDefaults(invalidObj as OObject))
+      .toThrow(new TypeError('Expected Object, got string testing'))
+  })
+})