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_util.c

@@ -1,3 +1,5 @@
+#include "dat.h"
+#include "fn.h"
 #include "test.h"
 
 Str
@@ -20,3 +22,83 @@ checkstr(struct ct *t, char *where, char *want, Str *got)
 	return CT_ERRORF(t, "%s: want \"%s\", got \"%s\"",
 		where, want, buf);
 }
+
+void
+checkenginepreedit(struct ct *t, char *want)
+{
+	Str preedit;
+
+	testenginepreedit(&preedit);
+	checkstr(t, "engine preedit", want, &preedit);
+}
+
+static void
+pumpthread(void *arg)
+{
+	Pump *p;
+	Keyreq req;
+	uchar token;
+	Alt alts[] = {
+		{nil, &req, CHANRCV, nil},
+		{nil, &token, CHANRCV, nil},
+		{nil, nil, CHANEND, nil},
+	};
+
+	p = arg;
+	alts[0].c = keyc;
+	alts[1].c = p->stop;
+	for(;;)
+		switch(alt(alts)){
+		case 0:
+			chansend(p->trace, &req);
+			if(p->holdop == Pumpall || p->holdop == req.op)
+				chanrecv(p->go, &token);
+			testenginehandle(&req);
+			break;
+		case 1:
+			chansend(p->done, &token);
+			return;
+		}
+}
+
+/* ntrace is the trace channel's depth: 0 makes every trace a rendezvous. */
+void
+pumpstart(Pump *p, int ntrace)
+{
+	memset(p, 0, sizeof *p);
+	p->trace = chancreate(sizeof(Keyreq), ntrace);
+	p->go = chancreate(sizeof(uchar), 0);
+	p->stop = chancreate(sizeof(uchar), 0);
+	p->done = chancreate(sizeof(uchar), 0);
+	p->holdop = Pumpnone;
+	/* Its own proc: tests block in socket I/O while the engine runs. */
+	proccreate(pumpthread, p, 8192);
+	p->active = 1;
+}
+
+void
+pumphold(Pump *p, int op)
+{
+	p->holdop = op;
+}
+
+/* Every held request must have been let go before stopping. */
+void
+pumpstop(Pump *p)
+{
+	Keyreq req;
+	uchar token;
+
+	if(!p->active)
+		return;
+	while(channbrecv(p->trace, &req) > 0)
+		;
+	token = 0;
+	chansend(p->stop, &token);
+	chanrecv(p->done, &token);
+	chanfree(p->trace);
+	chanfree(p->go);
+	chanfree(p->stop);
+	chanfree(p->done);
+	p->active = 0;
+}