Get the tracer right for metacov

2 files changed, 6 insertions, 2 deletions

diff --git a/coverage/collector.py b/coverage/collector.py
index 0348bb72..c1560902 100644
--- a/coverage/collector.py
+++ b/coverage/collector.py
@@ -247,7 +247,11 @@ class Collector(object):
     def stop(self):
         """Stop collecting trace information."""
         assert self._collectors
-        assert self._collectors[-1] is self
+        assert self._collectors[-1] is self, (
+            "Expected current collector to be %r, but it's %r" % (
+                self, self._collectors[-1],
+            )
+        )
 
         self.pause()
         self.tracers = []
diff --git a/igor.py b/igor.py
index 8e9410bc..17f4114b 100644
--- a/igor.py
+++ b/igor.py
@@ -61,7 +61,6 @@ def run_tests(tracer, *nose_args):
         return
 
     print_banner(label)
-    os.environ["COVERAGE_TEST_TRACER"] = tracer
     nose_args = ["nosetests"] + list(nose_args)
     nose.core.main(argv=nose_args)
 
@@ -136,6 +135,7 @@ def do_combine_html():
 
 def do_test_with_tracer(tracer, *noseargs):
     """Run nosetests with a particular tracer."""
+    os.environ["COVERAGE_TEST_TRACER"] = tracer
     if os.environ.get("COVERAGE_COVERAGE", ""):
         return run_tests_with_coverage(tracer, *noseargs)
     else: