When I make some changes in a JAVA file, infinitest launch the tests of the current project (which is what I expect, it takes only few seconds).
After a timeout (I don't know exactly), infinitest begins to run all the tests from all the projects in my workspace, is it possible to avoid that? (it takes several hours)
Infinitest should not trigger tests for other projects without changes on their dependencies. If you have a reproducible case please file a bug against Infinitest project.
Infinitest for Eclipse currently does not support enabling Infinitest only for part of the workspace. This requirement is already tracked by issue 140. What you can do however is define an infinitest.filters to filter out test in the projects you don't want to test. See http://infinitest.github.io/doc/eclipse#configuring-infinitest