Rename toString in wrapper_test

test/wrapper_test.dart

@@ -36,7 +36,9 @@ abstract class Expector {
     testInvocations(m, m2);
   }));
 
-  toString() => new _Equals(equals = getWrappedObject((m2) {
+  // dartanalyzer complains if this method is named `toString()`, since, if it
+  // truly overrides Object's `toString()`, it should return a String.
+  asString() => new _Equals(equals = getWrappedObject((m2) {
     testInvocations(TO_STRING_INVOCATION, m2);
   }));
 }
@@ -174,7 +176,7 @@ void main() {
     expect.toList(growable: true).equals.toList(growable: true);
     expect.toList(growable: false).equals.toList(growable: false);
     expect.toSet().equals.toSet();
-    expect.toString().equals.toString();
+    expect.asString().equals.toString();
     expect.where(func1).equals.where(func1);
   }
 
@@ -260,7 +262,7 @@ void main() {
     expect.putIfAbsent(val, func0).equals.putIfAbsent(val, func0);
     expect.remove(val).equals.remove(val);
     expect.values.equals.values;
-    expect.toString().equals.toString();
+    expect.asString().equals.toString();
   }
 
   // Runs tests of Set behavior.