To advance Java programming educations, we have developed the Java programming learning assistant system (JPLAS) that can verify the correctness of the code from a student automatically using the test-driven development (TDD) method. Then, to register a new assignment in JPLAS, teachers are required to write the test code in addition to the reference source code. Unfortunately, most teachers at schools are not accustomed to writing test codes. In this paper, we propose a test code generation tool that automatically generates the test cases from the reference source code by extracting the outputs for given inputs using functions in JUnit. As assignments for Java novice students, the code that contains standard inputs/outputs is emphasized. For evaluation, we collected 97 codes containing standard inputs/outputs from Java programming text books or Web sites. The experimental result has shown that the proposed tool correctly generated the test codes for them except for one code using a random generator.