Which of the following levels is available for Apex tests in Salesforce?

The concept of Apex test levels in Salesforce is essential for ensuring the correct execution and validation of tests within the Salesforce environment. Among the options provided, "NoTestRun" is a valid level that specifies that no tests should be executed during the deployment process.

In the context of Apex testing, "NoTestRun" allows developers to deploy code changes while skipping the execution of tests. This can be particularly useful in scenarios where you may not want to run tests, such as in certain administrative or configuration updates where test execution is not a requisite.

The other levels, such as "TestAllRun," "RunAllTestsInProcess," and "ExecuteAllTests," are focused on executing tests. "TestAllRun" and "ExecuteAllTests" are designed to run all tests in the organization, while "RunAllTestsInProcess" specifies running all tests in the same process as the deployment, which may impact system resources and execution time. Thus, "NoTestRun" is the only option that aligns with the intention of avoiding test execution altogether.