Unit testing is a practical approach for increasing the correctness and quality of software; but writing unit test code is exhausting and tedious job; and requires a great deal of time and effort. So even with the use of frameworks for writing and running unit test such as JUnit this will need a great deal of time and effort. As a consequence, there is a pressure in writing testing code. So we present in this paper a new method to generate unit testing automatically in order to speed up the testing process and reduce the cost. We have implemented this method on the Java programming language, where we write a new specification called JFS describes the behavior of the function in terms of input and output. This specification is written inside the code class and is independent of the code, and it can be written before starting the code phase and thus achieve the principle TDD Test-Driven Development which is based on written test-first in order to improve the development process. After writing specification we will generate test classes for the execution of unit testing (we used JUnit as framework to execute unit testing) based on the new specification.