How Can I Effectively Stub Out `time.Now()` Globally for Testing in Go?

Stubbing Out time.Now() Globally: Exploring Alternatives

In testing code that depends on time-sensitive functionalities, the need arises to simulate time progression. While implementing a custom time interface can be an effective solution, its usage can become cumbersome due to the need to pass a variable around to track actual elapsed time.

Custom Time Package

As an alternative, consider creating a custom time package that wraps around the standard library's time package. This approach allows you to seamlessly switch between the real-time implementation and a mock implementation for testing. For example:

// custom_time.go
package custom_time

import (
    "time"
    "sync"
)

var (
    mockTime time.Time
    mockMutex sync.Mutex
)

func SetMockTime(t time.Time) {
    mockMutex.Lock()
    mockTime = t
    mockMutex.Unlock()
}

func ResetMockTime() {
    mockMutex.Lock()
    mockTime = time.Time{}
    mockMutex.Unlock()
}

func Now() time.Time {
    mockMutex.Lock()
    defer mockMutex.Unlock()
    if mockTime != (time.Time{}) {
        return mockTime
    }
    return time.Now()
}

Advantages of Custom Package

• Global Scope: This approach stubs out time.Now() for all instances of the time package within the test scope.
• Easy Toggling: Switching between real and mock time is straightforward using the SetMockTime and ResetMockTime functions.
• Maintainability: Keeping a separate time package for testing purposes enhances code organization.

Disadvantages of Custom Package

• Additional Abstraction: May introduce a slight overhead due to the additional layer of abstraction.

Caution Against System Clock Modification

It is strongly advised against modifying the system clock during tests to simulate time progression. This can lead to unpredictable consequences for other system components that rely on the accurate system time.

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