Flasky Test TestOTLPWriteHandler

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Introduction

In this article, we will delve into the issue of a flaky test, specifically TestOTLPWriteHandler, in the Prometheus project. The test is failing due to a race condition, resulting in inconsistent test results. We will analyze the test output, identify the root cause of the issue, and provide a solution to make the test more robust.

Test Output

The test output indicates that the test is failing due to a "Sample not found" error. The expected and actual values are compared, and the actual values do not match the expected values. The test is failing for three test cases: NoTranslation, UnderscoreEscapingWithSuffixes, and NoUTF8EscapingWithSuffixes.

=== RUN   TestOTLPWriteHandler
=== RUN   TestOTLPWriteHandler/NoTranslation
    write_test.go:474: 
        	Error Trace:	D:/a/prometheus/prometheus/storage/remote/write_test.go:491
        	            				D:/a/prometheus/prometheus/storage/remote/write_test.go:474
        	Error:      	Sample not found: 
        	            	expected: {[{__name__ test.counter} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750664 10}
        	            	actual  : [{[{__name__ test.histogram_sum} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750663 30} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 0}] 1745762750663 2} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 2}] 1745762750663 6} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 3}] 1745762750663 8} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 4}] 1745762750663 10} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 5}] 1745762750663 12} {[{__name__ test.gauge} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750663 10} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 1}] 1745762750663 4} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le +Inf}] 1745762750663 10} {[{__name__ target_info} {host.name test-host} {instance test-instance} {job test-service}] 1745762750663 1}]
        	Test:       	TestOTLPWriteHandler/NoTranslation
=== RUN   TestOTLPWriteHandler/UnderscoreEscapingWithSuffixes
    write_test.go:474: 
        	Error Trace:	D:/a/prometheus/prometheus/storage/remote/write_test.go:491
        	            				D:/a/prometheus/prometheus/storage/remote/write_test.go:474
        	Error:      	Sample not found: 
        	            	expected: {[{__name__ test_counter_total} {foo_bar baz} {instance test-instance} {job test-service}] 1745762750664 10}
        	            	actual  : [{[{__name__ test_histogram_sum} {foo_bar baz} {instance test-instance} {job test-service}] 1745762750663 30} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le 0}] 1745762750663 2} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le 1}] 1745762750663 4} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le 2}] 1745762750663 6} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le 5}] 1745762750663 12} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le +Inf}] 1745762750663 10} {[{__name__ target_info} {host_name test-host} {instance test-instance} {job test-service}] 1745762750663 1} {[{__name__ test_counter_total} {foo_bar baz} {instance test-instance} {job test-service}] 1745762750663 10} {[{__name__ test_histogram_count} {foo_bar baz} {instance test-instance} {job test-service}] 1745762750663 10} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le 3}] 1745762750663 8} {[{__name__ test_histogram_bucket} {foo_bar baz} {instance test-instance} {job test-service} {le 4}] 1745762750663 10} {[{__name__ test_gauge} {foo_bar baz} {instance test-instance} {job test-service}] 1745762750663 10}]
        	Test:       	TestOTLPWriteHandler/UnderscoreEscapingWithSuffixes
=== RUN   TestOTLPWriteHandler/NoUTF8EscapingWithSuffixes
    write_test.go:474: 
        	Error Trace:	D:/a/prometheus/prometheus/storage/remote/write_test.go:491
        	            				D:/a/prometheus/prometheus/storage/remote/write_test.go:474
        	Error:      	Sample not found: 
        	            	expected: {[{__name__ test.counter_total} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750664 10}
        	            	actual  : [{[{__name__ test.counter_total} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750663 10} {[{__name__ test.gauge} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750663 10} {[{__name__ test.histogram_sum} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750663 30} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 0}] 1745762750663 2} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 2}] 1745762750663 6} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 3}] 1745762750663 8} {[{__name__ test.histogram_count} {foo.bar baz} {instance test-instance} {job test-service}] 1745762750663 10} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 1}] 1745762750663 4} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 4}] 1745762750663 10} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le 5}] 1745762750663 12} {[{__name__ test.histogram_bucket} {foo.bar baz} {instance test-instance} {job test-service} {le +Inf}] 1745762750663 10} {[{__name__ target_info} {host.name test-host} {instance test-instance} {job test-service}] 1745762750663 1}]
        	Test:       	TestOTLPWriteHandler/NoUTF8EscapingWithSuffixes
--- FAIL: TestOTLPWriteHandler (0.00s)
    --- FAIL: TestOTLPWriteHandler/NoTranslation (0.00s)
    --- FAIL: TestOTLPWriteHandler/UnderscoreEscapingWithSuffixes (0.00s)
    --- FAIL: TestOTLPWriteHandler/NoUTF8EscapingWithSuffixes (0.00s)

Root Cause of the Issue

The root cause of the issue is a race condition between the test and the underlying system. The test is expecting a specific timestamp, but the actual timestamp is different due to the race condition. The timestamp is 1745762750664 in the expected value, but it is 1745762750663 in the actual value.

Solution

To solve this issue, we need to ensure that the test and the underlying system are synchronized. We can achieve this by using a synchronization mechanism, such as a mutex, to ensure that the test and the underlying system are not executing concurrently.

Q&A: Understanding the Issue and Its Solutions

Q: What is the issue with the TestOTLPWriteHandler test? A: The issue with the TestOTLPWriteHandler test is a race condition that results in inconsistent test results. The test is expecting a specific timestamp, but the actual timestamp is different due to the race condition.

Q: What is a race condition? A: A race condition is a situation where two or more threads or processes are competing for the same resource, resulting in unpredictable behavior. In this case, the test and the underlying system are competing for the same resource, resulting in a race condition.

Q: How can we solve the issue of the TestOTLPWriteHandler test? A: We can solve the issue of the TestOTLPWriteHandler test by using a synchronization mechanism, such as a mutex, to ensure that the test and the underlying system are not executing concurrently. Alternatively, we can use a more robust testing framework that can handle race conditions.

Q: What is a mutex? A: A mutex (short for "mutual exclusion") is a synchronization mechanism that allows only one thread or process to access a shared resource at a time. By using a mutex, we can ensure that the test and the underlying system are not executing concurrently, preventing the race condition.

Q: How can we use a mutex to solve the issue of the TestOTLPWriteHandler test? A: We can use a mutex to solve the issue of the TestOTLPWriteHandler test by acquiring the mutex before executing the test and releasing the mutex after the test is complete. This will ensure that the test and the underlying system are not executing concurrently, preventing the race condition.

Q: What are some other solutions to the issue of the TestOTLPWriteHandler test? A: Some other solutions to the issue of the TestOTLPWriteHandler test include:

  • Using a more robust testing framework that can handle race conditions
  • Implementing a retry mechanism to retry the test if it fails due to a race condition
  • Using a different synchronization mechanism, such as a semaphore or a lock

Q: How can we implement a retry mechanism to solve the issue of the TestOTLPWriteHandler test? A: We can implement a retry mechanism to solve the issue of the TestOTLPWriteHandler test by retrying the test if it fails due to a race condition. We can use a loop to retry the test a specified number of times, and if the test still fails after the specified number of retries, we can fail the test.

Q: What are some best practices for testing in a concurrent environment? A: Some best practices for testing in a concurrent environment include:

  • Using a synchronization mechanism to ensure that tests are not executing concurrently
  • Implementing a retry mechanism to retry tests if they fail due to a race condition
  • Using a more robust testing framework that can handle race conditions
  • Testing in a controlled environment to minimize the risk of race conditions

Q: How can we ensure that our tests are robust and reliable in a concurrent environment? A: We can ensure that our tests are robust and reliable in a concurrent environment by:

  • Using a mechanism to ensure that tests are not executing concurrently
  • Implementing a retry mechanism to retry tests if they fail due to a race condition
  • Using a more robust testing framework that can handle race conditions
  • Testing in a controlled environment to minimize the risk of race conditions
  • Regularly reviewing and updating our tests to ensure that they are still relevant and effective.