Add scheduling by test file.

xdist/scheduler/__init__.py

@@ -1,3 +1,4 @@
 from xdist.scheduler.each import EachScheduling  # noqa
 from xdist.scheduler.load import LoadScheduling  # noqa
 from xdist.scheduler.loadscope import LoadScopeScheduling  # noqa
+from xdist.scheduler.filescope import LoadFileScheduling  # noqa

xdist/scheduler/filescope.py

@@ -0,0 +1,52 @@
+from . import LoadScopeScheduling
+from py.log import Producer
+
+
+class LoadFileScheduling(LoadScopeScheduling):
+    """Implement load scheduling across nodes, but grouping test test file.
+
+    This distributes the tests collected across all nodes so each test is run
+    just once.  All nodes collect and submit the list of tests and when all
+    collections are received it is verified they are identical collections.
+    Then the collection gets divided up in work units, grouped by test file,
+    and those work units get submitted to nodes.  Whenever a node finishes an
+    item, it calls ``.mark_test_complete()`` which will trigger the scheduler
+    to assign more work units if the number of pending tests for the node falls
+    below a low-watermark.
+
+    When created, ``numnodes`` defines how many nodes are expected to submit a
+    collection. This is used to know when all nodes have finished collection.
+
+    This class behaves very much like LoadScopeScheduling, but with a file-level scope.
+    """
+
+    def __init(self, config, log=None):
+        super(LoadFileScheduling, self).__init__(config, log)
+        if log is None:
+            self.log = Producer('loadfilesched')
+        else:
+            self.log = log.loadfilesched
+
+    def _split_scope(self, nodeid):
+        """Determine the scope (grouping) of a nodeid.
+
+        There are usually 3 cases for a nodeid::
+
+            example/loadsuite/test/test_beta.py::test_beta0
+            example/loadsuite/test/test_delta.py::Delta1::test_delta0
+            example/loadsuite/epsilon/__init__.py::epsilon.epsilon
+
+        #. Function in a test module.
+        #. Method of a class in a test module.
+        #. Doctest in a function in a package.
+
+        This function will group tests with the scope determined by splitting
+        the first ``::`` from the left. That is, test will be grouped in a
+        single work unit when they reside in the same file.
+         In the above example, scopes will be::
+
+            example/loadsuite/test/test_beta.py
+            example/loadsuite/test/test_delta.py
+            example/loadsuite/epsilon/__init__.py
+        """
+        return nodeid.split('::', 1)[0]

xdist/scheduler/loadscope.py

@@ -373,12 +373,12 @@ class LoadScopeScheduling:
         extra_nodes = len(self.nodes) - len(self.workqueue)
 
         if extra_nodes > 0:
-            self.log('Shuting down {} nodes'.format(extra_nodes))
+            self.log('Shuting down {0} nodes'.format(extra_nodes))
 
             for _ in range(extra_nodes):
                 unused_node, assigned = self.assigned_work.popitem(last=True)
 
-                self.log('Shuting down unused node {}'.format(unused_node))
+                self.log('Shuting down unused node {0}'.format(unused_node))
                 unused_node.shutdown()
 
         # Assign initial workload