Where on a Maven build should a test framework reside - src/test/java or src/main/java?

I understand from the previous answers on this site that, for Maven builds:

src/main/java will be deployed to production whereas src/test/java will not be.
src/main/java contains the main application whereas src/test/java will contain code to test the main app

Now my question is, when writing a test framework, which approach is better/worse:

Test framework itself will be the main app - hence it will reside on src/main/java?
Test framework will only be used to test the main app - hence will reside on src/main/java?

Somehow getting stuck on visualizing this properly -

Approach 1 seems to be correct as a test framework will be the main purpose of the build hence that will be the main app.

But then somehow I cannot imagine a test framework being deployed to production.
Approach 2 seems to be correct, but then if the main purpose is to write a test framework then what will go inside src/main/java? Will that be empty or non-existing for my test framework app?

Any suggestions on this would be helpful.

Solution

I think you're going astray with

src/main/java will be deployed to production whereas src/test/java will not be.

I would rephrase it as

src/main/java contains the code that consumers of the module will use (it is the purpose of your module)

If your module is about something that an end user works with it will go into production.
If your module is a testing framework then it will not go into production (in the sense of being deployed onto a server or on client machines), but other modules will use it, so the testing framework should be in src/main/java

(This assumes that you build the testing framework as a separate module)

If you need real life examples, you don't need to look any further than JUnit (the legendary testing framework)

Prefer to work with TestNG? The code for TestNG is in a submodule "core", but even then: