"Operation '", op.node.DebugString(), "' was changed by ",
          mutation_type,
          " after it was run by a session. This mutation will have no effect, "
          "and will trigger an error in the future. Either don't modify "
          "nodes after running them or create a new session.");
    }
  }
}

namespace {

In an expression switch,
the switch expression is evaluated and
the case expressions, which need not be constants,
are evaluated left-to-right and top-to-bottom; the first one that equals the
switch expression
triggers execution of the statements of the associated case;
the other cases are skipped.
If no case matches and there is a "default" case,
its statements are executed.

             * performed in the order they were provided to the constructor. Verify
             * that as a sanity check:
             */
            assertFalse(future2.isCancelled());
            // Now attempt to trigger the exception:
            future2.set(DATA2);
          }
        },
        directExecutor());
    assertTrue(compound.cancel(false));
    assertTrue(compound.isCancelled());