strengthen core unit tests

Add table-driven dictionary miss and language-switch state coverage, regress stale candidates after backspace, and clear them before dictionary refresh. Keep IPC and runtime-created file checks outside the unit runner.

tests/dict_test.c

@@ -51,3 +51,38 @@ cleanup:
 	hmapfree(lang->dict);
 	lang->dict = saved;
 }
+
+void
+dictionary_misses_clear_result(struct ct *t)
+{
+	static const struct {
+		char *name;
+		char *key;
+		char *pre;
+	} cases[] = {
+		{ "empty key", "", "empty-preedit" },
+		{ "missing key", "missing", "missing-preedit" },
+	};
+	Dictreq req;
+	Dictres res;
+	Hmap *saved;
+	Lang *lang;
+	int i;
+
+	lang = getlang(LangJP);
+	saved = lang->dict;
+	lang->dict = hmapalloc(1);
+	for(i = 0; i < nelem(cases); i++){
+		memset(&res, 0xa5, sizeof res);
+		req.key = mkstr(cases[i].key);
+		req.pre = mkstr(cases[i].pre);
+		req.lang = LangJP;
+		dictlookup(&req, &res);
+		if(res.nkouho != 0)
+			CT_ERRORF(t, "%s: want 0 candidates, got %d",
+				cases[i].name, res.nkouho);
+		checkstr(t, cases[i].name, cases[i].pre, &res.key);
+	}
+	hmapfree(lang->dict);
+	lang->dict = saved;
+}