Add a magical function testinfra_hosts_update to update

list of hosts inside module.

The key useful scenario is filtering out hosts from
automatically generated host lists (f.e. from ansible inventory
based on group names).

This allows to create a tool to update this list, f.e. to
implement 'run_once' policy.

Author: amarao

doc/source/invocation.rst

@@ -35,6 +35,12 @@ You can also set hosts per test module::
         [....]
 
 
+If you need to filter or update generated host list (f.e. after ["ansible://somegroup"]),
+you can use testinfra_hosts_update function:
+
+    def testinfra_hosts_update(host_list):
+        return [host_list[0]]
+
 
 Parallel execution
 ~~~~~~~~~~~~~~~~~~

testinfra/plugin.py

@@ -117,6 +117,10 @@ def pytest_generate_tests(metafunc):
             ansible_inventory=metafunc.config.option.ansible_inventory,
             force_ansible=metafunc.config.option.force_ansible,
         )
+        if hasattr(metafunc.module, "testinfra_hosts_update"):
+            if not metafunc.module.testinfra_update.callable():
+                pytest.fail("testinfra_hosts_update must be a function")
+        params = metafunc.module.testinfra_hosts_update(params)
         params = sorted(params, key=lambda x: x.backend.get_pytest_id())
         ids = [e.backend.get_pytest_id() for e in params]
         metafunc.parametrize(