A Technology Compatibility Kit (TCK) is a suite of tests that at least nominally checks a particular alleged implementation of a Java Specification Request (JSR) for compliance.
They usually (but not always) consist of a graphical host application which communicates over TCP/IP with the device or Java virtual machine that is under test.
This decoupling enables TCKs to be used to test virtual machines on devices such as CLDC mobile phones which do not have the power to run the full TCK host application.
The first great milestone is to get the TCK running in the first place, which necessarily involves the Java implementation and underlying networking stack having a certain level of maturity.
[6] The JavaTest harness tool is today the most common unit testing framework used to verify the implementation compliance.
On November 9, 2010, the Apache Software Foundation threatened to withdraw from the Java Community Process if they were not granted a TCK license for Harmony without additional restrictions.