Fix test failures involving contextvars. (#96)

Author: a-feld

opentelemetry-sdk/tests/trace/test_trace.py

@@ -112,8 +112,7 @@ def test_start_span_explicit(self):
             self.assertIsNotNone(child.end_time)
 
     def test_span_members(self):
-        context = contextvars.ContextVar('test_span_members')
-        tracer = trace.Tracer(context)
+        tracer = trace.Tracer('test_span_members')
 
         other_context1 = trace_api.SpanContext(
             trace_id=trace.generate_trace_id(),