What is the better way to mock date using mockk

Question

Emil Kantis · Answer

why would you need to do that

Recca Chao · Answer

to separate my test and the current time

Quincy · Answer

Use `java time Clock` if you are on the JVM

Quincy · Answer

See <https kotlinlang slack com archives C9EJFT6DB p1631801269005500 thread ts=1631800907 005200 amp cid=C9EJFT6DB> for more info

Emil Kantis · Answer

Or `object Time fun now = Instant now ` for instance and you can easily do `mockkObject Time ` `every Time now returns myTimestamp`

Emil Kantis · Answer

as < Quincy> mentions in the linked thread depending your use case

Recca Chao · Answer

thanks < Emil Kantis> < Quincy>

Quincy · Answer

You re welcome

Recca Chao · Answer

My current test code ``` val fixedClock = Clock fixed Instant parse 2022 01 01T23 59 59Z ZoneId of UTC mockkStatic Clock class every Clock systemUTC returns fixedClock Assert assertThat isValidDate `is` false ```

Quincy · Answer

You don t need to mock the Clock itself Using the fixed clock gives you control over how timestamps are created Now what you need to do is ensure the SUT takes a Clock as a parameter and uses that Clock to create timestamps

Quincy · Answer

```class Sut private val clock Clock fun doSomething OffsetDateTime return OffsetDateTime now clock ```

Quincy · Answer

For example with the above class we can now write a test that can take control of the timestamp creation

Quincy · Answer

```fun `my test` val now = Instant of 1L val clock = Clock fixed now assertThat Sut clock doSomething equalTo OffsetDateTime of ```

Quincy · Answer

Something like that

Quincy · Answer

This give you the ability to let the production code use the real system clock when running in production but within tests you can specify the behavior of the clock And you don t need to mock anything

Recca Chao · Answer

understood I think this is a better way to invert the dependency thanks again

Quincy · Answer

You re welcome again slightly smiling face

thanksforallthefish · Answer

yesterday there was a similar question in < CT0G9SD7Z|kotest> if you are using that testing framework you can also wrap your test with `withConstantNow Instant now ` behind the scene it uses `mockkStatic` so it only works when in your code you do `val date = Instant now ` and it won t with `val date = LocalDate now ` you can also do `withConstantNow LocalDate now ` or every other time setting instruction though personally I still prefer to use a clock not a big fan of static mocking in general as much as I would actually remove it from the library