[CODE QUALITY]: Resolve Unittest Compilation Warnings

[yyuuttaaoo]

Description

We have observed a significant number of compilation warnings in the current unittest suite. While the main codebase has successfully achieved zero warnings, the unittest code still generates numerous warnings during the build process. These warnings, although not critical, can obscure more serious issues and hinder our ability to maintain high code quality.

Rationale

1. Detecting Errors Early: Compilation warnings often act as early indicators of potential bugs or issues, such as type mismatches or unintended behavior. By addressing these warnings, we can catch and fix low-level errors before they escalate into larger problems.
2. Improving Code Quality: A codebase free of warnings is easier to maintain and understand. It reduces noise for developers, allowing them to focus on real issues rather than sifting through numerous benign warnings.
3. Consistency Across Codebase: Achieving zero warnings in the unittests will bring consistency across the entire codebase, aligning with the existing main code practices.
4. Facilitating Contributions: A clean build environment with no warnings is more welcoming to new contributors. It sets a standard for code quality and encourages adherence to best practices.
5. Ensuring Reliability: Unittests play a critical role in validating the correctness of our software. Ensuring their compilation is free of warnings enhances overall reliability and confidence in the tests themselves.

Proposal

We invite the community to contribute towards resolving these unittest compilation warnings. This would involve:

• Identifying and Analyzing: Review the warnings to understand their causes, and determine the appropriate fixes, such as correcting type mismatches or adjusting test logic.
• Implementing Fixes: Modify the unittest code to eliminate the warnings, ensuring that all changes maintain or improve the current test coverage and reliability.
• Review and Testing: Submit pull requests with the proposed changes for review. Ensure that the fixes are verified and that the unittest suite passes without introducing new warnings or errors.

Thank you for your efforts to improve the code quality and maintainability of our project.

Examples of Current Warnings

Here are some examples of the warnings being generated:

[build] /workspaces/loongcollector-qianlu/core/unittest/processor/ProcessorSplitMultilineLogStringNativeUnittest.cpp:327:5:   required from here
[build] /opt/logtail/deps/include/gtest/gtest.h:1444:11: warning: comparison of integer expressions of different signedness: 'const int' and 'const long unsigned int' [-Wsign-compare]
[build]  1444 |   if (lhs == rhs) {
[build]       |       ~~~~^~~~~~
[build] In file included from /workspaces/loongcollector-qianlu/core/unittest/Unittest.h:24,
[build]                  from /workspaces/loongcollector-qianlu/core/unittest/prometheus/PromAsynUnittest.cpp:5:
[build] /opt/logtail/deps/include/gtest/gtest.h: In instantiation of 'testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = long int]':
[build] /opt/logtail/deps/include/gtest/gtest.h:1472:23:   required from 'static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = long int; bool lhs_is_null_literal = false]'
[build] /workspaces/loongcollector-qianlu/core/unittest/prometheus/PromAsynUnittest.cpp:20:9:   required from here
[build] /opt/logtail/deps/include/gtest/gtest.h:1444:11: warning: comparison of integer expressions of different signedness: 'const long unsigned int' and 'const long int' [-Wsign-compare]
[build]  1444 |   if (lhs == rhs) {
[build]       |       ~~~~^~~~~~
[build] In file included from /workspaces/loongcollector-qianlu/core/unittest/Unittest.h:24,
[build]                  from /workspaces/loongcollector-qianlu/core/unittest/processor/ProcessorFilterNativeUnittest.cpp:18:
[build] /opt/logtail/deps/include/gtest/gtest.h: In instantiation of 'testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = int; T2 = long unsigned int]':
[build] /opt/logtail/deps/include/gtest/gtest.h:1472:23:   required from 'static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = int; T2 = long unsigned int; bool lhs_is_null_literal = false]'
[build] /workspaces/loongcollector-qianlu/core/unittest/processor/ProcessorFilterNativeUnittest.cpp:71:5:   required from here
[build] /opt/logtail/deps/include/gtest/gtest.h:1444:11: warning: comparison of integer expressions of different signedness: 'const int' and 'const long unsigned int' [-Wsign-compare]
[build]  1444 |   if (lhs == rhs) {
[build]       |       ~~~~^~~~~~
[build] In file included from /workspaces/loongcollector-qianlu/core/unittest/Unittest.h:24,
[build]                  from /workspaces/loongcollector-qianlu/core/unittest/input/InputNetworkObserverUnittest.cpp:24:
[build] /opt/logtail/deps/include/gtest/gtest.h: In instantiation of 'testing::AssertionResult testing::internal::CmpHelperEQ(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = int]':
[build] /opt/logtail/deps/include/gtest/gtest.h:1472:23:   required from 'static testing::AssertionResult testing::internal::EqHelper<lhs_is_null_literal>::Compare(const char*, const char*, const T1&, const T2&) [with T1 = long unsigned int; T2 = int; bool lhs_is_null_literal = false]'