Review the testing framework

Oct 13, 2025 by magicalceylontours.com 72 views

x/tools/gopls/internal/test/integration: Violates Testing.T.FailNow Precondition

Introduction

The Go programming language has a robust testing framework that allows developers to write and execute unit tests with ease. However, like any complex system, it is not immune to potential issues and edge cases. In this article, we will explore a specific problem related to the testing framework, specifically the testing.T.FailNow precondition, and how it is violated by the gopls integration test framework.

Understanding the Testing.T.FailNow Precondition

The documentation of the testing.T type in the Go standard library provides valuable insights into the behavior of the testing framework. According to the documentation, a test ends when its Test function returns or calls any of the methods FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. These methods, as well as the Parallel method, must be called only from the goroutine running the Test function.

// A test ends when its Test function returns or calls any of the methods
// FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. Those methods, as well as
// the Parallel method, must be called only from the goroutine running the
// Test function.

The Problem with gopls Integration Test Framework

The gopls integration test framework, located in the x/tools/gopls/internal/test/integration package, captures the root testing.T and uses it for many assertions (calls to t.Fatal) performed by the Env itself. However, it is common for integration tests to create new subtests using t.Run and then call methods of Env that call Env.T.Fatal.

// integration.Env captures the root testing.T and uses it for many assertions
// (calls to t.Fatal) performed by the Env itself.

This behavior results in the testing package emitting messages like the following:

testing.go:1682: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test

Is This a Real Problem?

It is unclear whether this is a real problem or if the testing package is already robust enough to handle this kind of misuse. However, it is essential to be aware of this potential issue and consider whether it is something that needs to be addressed.

Conclusion

In conclusion, the gopls integration test framework violates the testing.T.FailNow precondition by capturing the root testing.T and using it for many assertions performed by the Env itself. This behavior results in the testing package emitting messages indicating potential issues. While it is unclear whether this is a real problem, it is essential to be aware of this potential issue and consider whether it is something that needs to be addressed.

Recommendations

To address this issue, the following recommendations can be made:

Review the testing framework: Review the testing framework to ensure that it is robust enough to handle this kind of misuse.
Use a separate testing.T: Consider using a separate testing.T for each subtest to avoid violating the testing.T.FailNow precondition.
Avoid calling FailNow on a parent test: Avoid calling FailNow on a parent test from a subtest to prevent potential issues.

Example Use Case

Here is an example use case that demonstrates how to use a separate testing.T for each subtest:

func TestIntegration(t *testing.T) {
    // Create a new testing.T for each subtest
    t.Run("subtest1", func(t *testing.T) {
        // Perform assertions using the new testing.T
        if !someCondition() {
            t.Fatal("someCondition failed")
        }
    })

    t.Run("subtest2", func(t *testing.T) {
        // Perform assertions using the new testing.T
        if !someOtherCondition() {
            t.Fatal("someOtherCondition failed")
        }
    })
}

By following these recommendations and using a separate testing.T for each subtest, you can avoid violating the testing.T.FailNow precondition and ensure that your tests are robust and reliable.
x/tools/gopls/internal/test/integration: Violates Testing.T.FailNow Precondition

Q&A

Q: What is the testing.T.FailNow precondition?

A: The testing.T.FailNow precondition is a rule that states that a test ends when its Test function returns or calls any of the methods FailNow, Fatal, Fatalf, SkipNow, Skip, or Skipf. These methods, as well as the Parallel method, must be called only from the goroutine running the Test function.

Q: Why is the gopls integration test framework violating the testing.T.FailNow precondition?

A: The gopls integration test framework is capturing the root testing.T and using it for many assertions (calls to t.Fatal) performed by the Env itself. However, it is common for integration tests to create new subtests using t.Run and then call methods of Env that call Env.T.Fatal. This behavior results in the testing package emitting messages indicating potential issues.

Q: Is this a real problem or is the testing package already robust enough to handle this kind of misuse?

A: It is unclear whether this is a real problem or if the testing package is already robust enough to handle this kind of misuse. However, it is essential to be aware of this potential issue and consider whether it is something that needs to be addressed.

Q: What are the potential consequences of violating the testing.T.FailNow precondition?

A: Violating the testing.T.FailNow precondition can result in the testing package emitting messages indicating potential issues, such as:

testing.go:1682: test executed panic(nil) or runtime.Goexit: subtest may have called FailNow on a parent test

Q: How can I avoid violating the testing.T.FailNow precondition?

A: To avoid violating the testing.T.FailNow precondition, you can use a separate testing.T for each subtest. Here is an example use case that demonstrates how to use a separate testing.T for each subtest:

func TestIntegration(t *testing.T) {
    // Create a new testing.T for each subtest
    t.Run("subtest1", func(t *testing.T) {
        // Perform assertions using the new testing.T
        if !someCondition() {
            t.Fatal("someCondition failed")
        }
    })

    t.Run("subtest2", func(t *testing.T) {
        // Perform assertions using the new testing.T
        if !someOtherCondition() {
            t.Fatal("someOtherCondition failed")
        }
    })
}

Q: What are the benefits of using a separate testing.T for each subtest?

A: Using a separate testing.T for each subtest can help avoid violating the testing.T.FailNow precondition and ensure that your tests are robust and reliable. It can also make your tests more readable and maintainable by separating the assertions for each subtest.

Q: Can I use a single testing.T for all subtests?

A: While it is technically possible to use a single testing.T for all subtests, it is not recommended. Using a single testing.T can lead to complex and hard-to-debug test code, and may result in violating the testing.T.FailNow precondition.

Q: How can I determine if my tests are violating the testing.T.FailNow precondition?

A: You can determine if your tests are violating the testing.T.FailNow precondition by running your tests and checking the output for messages indicating potential issues. You can also use tools like go test -v to get more detailed output and help diagnose any issues.

Conclusion

In conclusion, the gopls integration test framework violates the testing.T.FailNow precondition by capturing the root testing.T and using it for many assertions performed by the Env itself. This behavior results in the testing package emitting messages indicating potential issues. To avoid violating the testing.T.FailNow precondition, you can use a separate testing.T for each subtest. By following these recommendations and using a separate testing.T for each subtest, you can ensure that your tests are robust and reliable.