Brian Foote and Joseph Yoder first popularized the Big Ball of Mud in their self-titled paper. Unlike the Spaghetti pattern, where the test suite can be separated into individual strands, Big Ball of Mud does not have any formal structures that will allow a distinction between any individual components. Test data and results are promiscuously shared amongst most distant and unrelated components until everything is global and mutable without warning. Unintentional test failures occur when a component is changed for a new test without the realization that hundreds of other tests depend on it. To exacerbate the problem, there is no easy way to find all of the interdependencies since everything is merged together like a piece of wet clay.

Adoption of this pattern is usually unintentional and stems from being developed over long periods of time with different individuals working on different pieces without any overall architectural plan. The initial success of just...