How do I mock time in tests in Go?

In Go, mocking time in tests can be accomplished by using interfaces and dependency injection. By creating a time provider interface, you can substitute the real time function with a mock implementation during testing. This allows you to control the flow of time within your tests, making them more predictable and reliable.

package main

import (
    "fmt"
    "time"
)

type TimeProvider interface {
    Now() time.Time
}

type RealTimeProvider struct{}

func (r RealTimeProvider) Now() time.Time {
    return time.Now()
}

func DoSomething(t TimeProvider) {
    currentTime := t.Now()
    fmt.Println("Current time:", currentTime)
}

// In tests
type MockTimeProvider struct {
    mockTime time.Time
}

func (m MockTimeProvider) Now() time.Time {
    return m.mockTime
}

func Example() {
    mockTimeProvider := MockTimeProvider{mockTime: time.Date(2023, 10, 1, 10, 0, 0, 0, time.UTC)}
    DoSomething(mockTimeProvider)
}