Avoid false positive Spring tests generated with Fuzzer

[EgorkaKulikov]

Description

Spring unit tests generated with symbolic engine avoid branches whis thisInstance == null if being null is actually impossible.
For example, because variable with @InjectMocks annotation is never null.

Fuzzer currently does not support this restrictions, so we generate tests like this:

///region FUZZER: ERROR SUITE for method useAbs(int)

@Test
@DisplayName("useAbs: x = -3 (mutated from -1) -> throw NullPointerException")
public void testUseAbsThrowsNPE() {
    /* This test fails because method [org.springframework.samples.math.MathUser.useAbs] produces [java.lang.NullPointerException]
        org.springframework.samples.math.MathUser.useAbs(MathUser.java:10) */
  mathUser.useAbs(-3);
}
///endregion

This test passes and writes that should fail :)

[alisevych]

@EgorkaKulikov
Let's consider the following questions:

1. Is it Ok to remove ALL tests on NPE in Spring Unit tests?
   What if Spring configuration is incorrect and this NPE will be thrown?
2. Terminology. Such cases are considered to be false positive - if I'm not mistaken.
   They are false positive to question: "Is there an error?"

[alisevych]

depends on #2321