Update StubInvocationUtilTest.java

[gzhao9]

Purpose of the Change

This PR is aimed at resolving the issue of duplicated creation of mock. This occurs in five test cases in StubInvocationUtilTest.java, as highlighted in issue # 13153.

Brief changelog

We created 5 reusable methods to create the mock, avoiding duplicate creation of the mock in 5 test cases.
We also set the five mock objects as class attributes and create them in @BeforeEach.
After removing duplicate mocks for 5 test cases, our refactoring reduced the number of lines of code by 76 lines, improving readability and maintainability.

Verifying this change

Checklist

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