A more thorough explanation:

The nexus test is a legal standard used to determine if a private person's actions can be considered state action and therefore be held liable for violating someone's constitutional rights. The test looks at whether the private person's conduct is closely related to the government's conduct and if the choice to undertake it can be considered that of the state.

For example, if a private security company is hired by a government agency to provide security at a public event and the security company uses excessive force against a protester, the nexus test would be used to determine if the security company's actions can be considered state action and if the protester's constitutional rights were violated.

The purpose of the nexus test is to ensure that constitutional standards are only applied when the state is responsible for the specific conduct being complained of. The test helps to determine if the state has exercised coercive power or provided significant encouragement to the private person's actions.