diff --git a/tests/Makefile b/tests/Makefile
index eb4b7ae..2fc4ce7 100644
--- a/tests/Makefile
+++ b/tests/Makefile
@@ -11,6 +11,7 @@ test: $(exebin)
 	./testcentury
 	./test_bits1to14
 
+JSON_L?=`pkg-config --libs json-c`
 PREFIX?=.
 ETCDIR?=etc/dcf77pi
 CFLAGS+=-Wall -D_POSIX_C_SOURCE=200809L -DETCDIR=\"$(PREFIX)/$(ETCDIR)\" \
@@ -22,8 +23,8 @@ testcentury: testcentury.o ../calendar.o
 	$(CC) -o $@ testcentury.o ../calendar.o
 test_bits1to14.o: ../bits1to14.h
 	$(CC) -fpic $(CFLAGS) -I.. -c test_bits1to14.c -o $@
-test_bits1to14: test_bits1to14.o ../bits1to14.o
-	$(CC) -o $@ test_bits1to14.o ../bits1to14.o
+test_bits1to14: test_bits1to14.o ../bits1to14.o ../input.o
+	$(CC) -o $@ test_bits1to14.o ../bits1to14.o ../input.o -lm $(JSON_L)
 
 clean:
 	rm -f $(objbin) $(exebin)
diff --git a/tests/test_bits1to14.c b/tests/test_bits1to14.c
index ec35e63..7a4e76b 100644
--- a/tests/test_bits1to14.c
+++ b/tests/test_bits1to14.c
@@ -2,12 +2,68 @@
 // SPDX-License-Identifier: BSD-2-Clause
 
 #include "bits1to14.h"
+#include "input.h"
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <sysexits.h>
 
 int
 main(int argc, char *argv[])
 {
+	unsigned in_buf[TPBUFLEN];
+	const unsigned *rb_ptr;
+	enum eTP tp_res[4] = { eTP_weather, eTP_unknown, eTP_unknown,
+	    eTP_alarm };
+	struct GB_result gbr;
+
+	srand(1); /* INSECURE random function, but C99-compliant */
+	for (int ofs = 0; ofs < 3; ofs++) {
+		for (unsigned type = 0; type < 4; type++) {
+			/* fill the buffer */
+			for (int i = 0; i < TPBUFLEN + 2; i++) {
+				/*
+				 * Calculate absolute position in buffer when
+				 * jumping in half-way a message.
+				 */
+				int k = i - 14 * ofs;
+				if (k < 0)
+					k += TPBUFLEN + 2;
+				if (k == 0) {
+					gbr.bitval = ((type & 1) == 1 ? ebv_1 :
+					    ebv_0);
+				} else if (k == 7) {
+					gbr.bitval = ((type & 2) == 2 ? ebv_1 :
+					    ebv_0);
+				} else {
+					int j = (k < 7) ? k - 1 : k - 2;
+					in_buf[j] = rand() % 2;
+					gbr.bitval = (in_buf[j] == 0 ? ebv_0 :
+					    ebv_1);
+				}
+				fill_thirdparty_buffer(k / 14, k % 14 + 1, gbr);
+			}
+
+			/* test retrieving the buffer */
+			rb_ptr = get_thirdparty_buffer();
+			for (unsigned i = 0; i < TPBUFLEN; i++) {
+				if (in_buf[i] != rb_ptr[i]) {
+					printf("%s: ofs %i type %u bit %u:"
+					   " %u should be %u\n", argv[0], ofs,
+					   type, i, rb_ptr[i], in_buf[i]);
+					return EX_SOFTWARE;
+				}
+			}
+
+			/* test retrieving the type */
+			enum eTP tp_type;
+			tp_type = get_thirdparty_type();
+			if (tp_type != tp_res[type]) {
+				printf("%s: ofs %i: type %i should be %i\n",
+				    argv[0], ofs, tp_type, tp_res[type]);
+				return EX_SOFTWARE;
+			}
+		}
+	}
 	return EX_OK;
 }