diff --git a/pytest_check_mk/file_loader.py b/pytest_check_mk/file_loader.py
index b201d03..4ef6c0a 100644
--- a/pytest_check_mk/file_loader.py
+++ b/pytest_check_mk/file_loader.py
@@ -1,7 +1,6 @@
 import imp
 import os
-
-
+from string import Template
 from pytest_check_mk import MissingFileError
 
 
@@ -31,8 +30,32 @@ def regex(r):
 snmp_scan_functions                = {} # SNMP autodetection
 active_check_info                  = {} # definitions of active "legacy" checks
 special_agent_info                 = {}
+
 '''
 
+# E.g. host_extra_conf_merged is a WATO function which is only available when the
+# check is run in MK's context. The same applies to the inventory rules etc.
+# We can monkeypatch these data in our test file only when they are present; monkey-
+# patch cannot create new data.
+
+# The following code gets appended to the module. All runtime relevant data and
+# functions must be initialised here.
+# Example (file: test_foobar.py):
+# mock_inventory_foobar_rules = [ ...(rules) ...]
+# monkeypatch.setattr(checks.module, "inventory_foobar_rules", mock_inventory_foobar_rules)
+
+WATO_DATA = Template('''
+# function to retrieve host relevant config
+def host_extra_conf_merged(self):
+    pass
+
+# WATO rules
+inventory_${name}_rules = { }
+
+def host_name():
+    return "localhost"
+''')
+
 
 def check_module_from_source(name, path):
     __tracebackhide__ = True
@@ -40,7 +63,9 @@ def check_module_from_source(name, path):
     if not os.path.exists(path):
         raise MissingFileError(path)
 
-    source = open(path, 'r').read()
+    source = open(path, 'r').read() + WATO_DATA.substitute({
+        'name': name
+    })
     code = compile(source, path, 'exec')
     module = imp.new_module(name)
 
diff --git a/pytest_check_mk/plugin.py b/pytest_check_mk/plugin.py
index ebc3918..a614bd9 100644
--- a/pytest_check_mk/plugin.py
+++ b/pytest_check_mk/plugin.py
@@ -13,9 +13,11 @@ def _get_check_name(request):
 
 @pytest.fixture
 def agents(request):
+    '''returns a checkMK agent instance'''
     return AgentDirectoryWrapper()
 
 
 @pytest.fixture
 def checks(request):
+    '''returns a checkMK check instance'''
     return create_check_file_wrapper(_get_check_name(request))