[PROPOSAL] Add guidelines for tests to maintainers.md file

What kind of business use case are you trying to solve? What are your requirements?

We need to define standards and guidelines around the tests for the contributions to improve the quality of the code.

What is the problem? What is preventing you from meeting the requirements?
Currently, we dont have any guidelines around tests hence code contributions and merges are very subjective at this point in time

What are you proposing? What do you suggest we do to solve the problem or improve the existing situation?
Suggest adding below section to https://github.com/opensearch-project/.github/blob/main/MAINTAINERS.md

Test the Changes

Check whether tests already exist in the project to test the contribution. If so, make sure to execute it every time before merging the changes. If the test doesn’t exist, understand the type of testing requirement ( Integration? Unit? Acceptance? ) for the contribution and see if we can re-use the framework by setting up a new testing harness for the project.

If adequate testing for a contribution does not exist, it is our responsibility to make sure the tests are added either by requesting the contributor to add one or more tests OR by adding the tests ourselves. If we are merging a fix, the added tests should fail without the fix. If we are merging an enhancement, we should make sure that the tests thoroughly exercise the new functionality.

What are your assumptions or prerequisites?
Describe any assumptions you may be making that would limit the scope of this proposal.

What are remaining open questions?
List questions that may need to be answered before proceeding with an implementation.

Start by reviewing the MAINTAINERS.md file in the opensearch-project/.github repository and compare the proposed “Test the Changes” section with its existing structure. Done means adding the agreed testing guidelines to that file after any open questions about the proposal are resolved.