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

Global Stubbing of time.Now()

In testing, it becomes crucial to control time-dependent aspects of code. However, stubbing out time.Now() globally can be challenging due to widespread usage across multiple code sections.

Suggested Approach: Custom Time Interface

The current implementation using a custom interface is an effective solution. Here's a summary of the approach:

1. Define a Clock interface with methods Now() and After(d time.Duration).
2. Create a concrete implementation (e.g., realClock) that behaves like the standard time package.
3. Create a mock implementation for testing (e.g., mockClock).

Alternatives

Changing the system clock during tests is strongly discouraged as it can lead to unforeseen dependencies.

Limitations

Stubbing out time.Now() globally has its limitations. For example, if the code under test uses third-party libraries that rely on system time, it may not be possible to override their behavior.

Benefits of Stateless Code

Designing code with as little statefulness as possible simplifies testing and facilitates concurrency. By separating functionality into testable, stateless components, it becomes easier to control time-sensitive aspects during tests.

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