Most companies have an environment specifically for testing. This is a great place to do extensive testing, such as nightly or off-peak regression runs. If someone has recently deployed buggy code to the environment, unit tests could catch the bug. Additionally, a test environment is often where you have the most control over your test data. However, this also means that other testers might change your data, so consider a good test data management strategy.

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Read "An Introduction To The Automation Test Wheel" by Kristin Jackvony in Ministry of Testing's Testing Planet