test: one engine pump and one preedit check for the white-box suites

server_test, ibus_test and xim_adapter_test each ran their own copy of
the same alt loop that stands in for imthread, and two of them had
private checkstr/checkenginepreedit variants. test_util.c now provides
Pump (trace, optional hold on a chosen op, stop) in its own proc so a
test may block in socket I/O while the engine runs, and test.h declares
the engine hooks once; every .c includes dat.h and fn.h itself as the
rest of the tree does. server_test's three copies of fixture setup and
teardown became serverbegin/serverend.

tests/test.h

@@ -1,11 +1,43 @@
+/* Included after dat.h and fn.h (or after the source under test). */
 #include "cutest/cutest.h"
-#include "dat.h"
-#include "fn.h"
 
 extern Lang testvi;
 
+/*
+ * A test's stand-in for imthread: handles engine requests from keyc,
+ * tracing each one first.  Requests whose op is holdop (every request
+ * when holdop is Pumpall) wait on go before the engine sees them.
+ */
+typedef struct Pump Pump;
+struct Pump
+{
+	Channel	*trace;
+	Channel	*go;
+	Channel	*stop;
+	Channel	*done;
+	int	holdop;
+	int	active;
+};
+
+enum
+{
+	Pumpnone = -1,
+	Pumpall = -2,
+};
+
 Str	mkstr(char*);
 int	checkstr(struct ct*, char*, char*, Str*);
+void	checkenginepreedit(struct ct*, char*);
+void	pumpstart(Pump*, int);
+void	pumphold(Pump*, int);
+void	pumpstop(Pump*);
+
+/* Engine internals reached through engine_test.c. */
+void	testengineinit(int);
+void	testenginehandle(Keyreq*);
+void*	testengineowner(void);
+void	testenginepreedit(Str*);
+void	testenginecaret(Caret*);
 
 void	str_init_utf8(struct ct*);
 void	str_edit_and_alias(struct ct*);