MachMultiprocess test: the child process must wait for the parent to finish

util/test/multiprocess.h

Index: util/test/multiprocess.h
diff --git a/util/test/multiprocess.h b/util/test/multiprocess.h
index 371d23f1d22421495be449f56da4f4bb7868cab4..781ec7c13a2fe88eeb6c60e4d26ef0760b5f5268 100644
--- a/util/test/multiprocess.h
+++ b/util/test/multiprocess.h
@@ -116,6 +116,10 @@ class Multiprocess {
   //! This method may be called by either the parent or the child process.
   //! Anything written to the write pipe in the partner process will appear
   //! on the this file descriptor in this process.
+  //!
+  //! It is an error to call this after CloseReadPipe() has been called.
+  //!
+  //! \return The read pipe’s file descriptor.
   int ReadPipeFD() const;
 
   //! \brief Returns the write pipe’s file descriptor.
@@ -123,8 +127,26 @@ class Multiprocess {
   //! This method may be called by either the parent or the child process.
   //! Anything written to this file descriptor in this process will appear on
   //! the read pipe in the partner process.
+  //!
+  //! It is an error to call this after CloseWritePipe() has been called.
+  //!
+  //! \return The write pipe’s file descriptor.
   int WritePipeFD() const;
 
+  //! \brief Closes the read pipe.
+  //!
+  //! This method may be called by either the parent or the child process. An
+  //! attempt to write to the write pipe in the partner process will fail with
+  //! `EPIPE` or `SIGPIPE`. ReadPipeFD() must not be called after this.
+  void CloseReadPipe();
+
+  //! \brief Closes the write pipe.
+  //!
+  //! This method may be called by either the parent or the child process. An
+  //! attempt to read from the read pipe in the partner process will indicate
+  //! end-of-file. WritePipeFD() must not be called after this.
+  void CloseWritePipe();
+
  private:
   //! \brief Runs the parent side of the test.
   //!