Replace 'the the' with 'the'

pkg/testing/lib/src/chain.dart

Index: pkg/testing/lib/src/chain.dart
diff --git a/pkg/testing/lib/src/chain.dart b/pkg/testing/lib/src/chain.dart
index 377c205c71bc42b9681435e6f763457b9ef45840..6496a81b3762acdee089e73e239b9aaf2cac20b4 100644
--- a/pkg/testing/lib/src/chain.dart
+++ b/pkg/testing/lib/src/chain.dart
@@ -150,7 +150,7 @@ abstract class ChainContext {
       /// asynchronous.
       ///
       /// If a step is asynchrouns the future returned from this function will
-      /// complete after the the first asynchronous step is scheduled.  This
+      /// complete after the first asynchronous step is scheduled.  This
       /// allows us to start processing the next test while an external process
       /// completes as steps can be interleaved. To ensure all steps are
       /// completed, wait for [futures].