How I could add dir to $PATH in Makefile?

I want to write a Makefile which would run tests. Test are in a directory './tests' and executable files to be tested are in the directory './bin'.

When I run the tests, they don't see the exec files, as the directory ./bin is not in the $PATH.

When I do something like this:

EXPORT PATH=bin:$PATH
make test

everything works. However I need to change the $PATH in the Makefile.

Simple Makefile content:

test all:
    PATH=bin:${PATH}
    @echo $(PATH)
    x

It prints the path correctly, however it doesn't find the file x.

When I do this manually:

$ export PATH=bin:$PATH
$ x

everything is OK then.

How could I change the $PATH in the Makefile?