Little’s Law | Glossary


Little’s Law states that in possession of a stable system, the average number of customers within it, is equal to the average rate of consumer arrivals multiplied by the average time a consumer usually spends in the overall system.

Little’s Law is expressed as L= λW.With ‘L’ as the average number of customers, ‘λ’ being the average arrival rate, and ‘W’ being the average time in the system. This law got it’s name on John Littel, who proposed it in the mid-1990s.

Further Reading

  • “Building Intuition: Insights From Basic Operations Management Models and Principles” (book), by John D.C Little.

xUnit Test Patterns | Book Series

xUnit Test Patterns is the definitive guide to writing automated tests using xUnit, the most popular unit testing framework in use today. Agile coach and test automation expert Gerard Meszaros describes 68 proven patterns for making tests easier to write, understand, and maintain. He then shows you how to make them more robust and repeatable–and far more cost-effective.

Loaded with information, this book feels like three books in one. The first part is a detailed tutorial on test automation that covers everything from test strategy to in-depth test coding. The second part, a catalog of 18 frequently encountered “test smells,” provides troubleshooting guidelines to help you determine the root cause of problems and the most applicable patterns. The third part contains detailed descriptions of each pattern, including refactoring instructions illustrated by extensive code samples in multiple programming languages.


Gerard Meszaros

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