diff --git a/cli/Makefile b/cli/Makefile
index a51fade7b..cad59b381 100644
--- a/cli/Makefile
+++ b/cli/Makefile
@@ -25,3 +25,4 @@ clean: lightning-cli-clean
 lightning-cli-clean:
 	$(RM) $(LIGHTNING-CLI_LIB_OBJS) $(DAEMON_JSMN_OBJS)
 
+include cli/test/Makefile
diff --git a/cli/test/.gitignore b/cli/test/.gitignore
new file mode 100644
index 000000000..9e48a0522
--- /dev/null
+++ b/cli/test/.gitignore
@@ -0,0 +1 @@
+run-large-input
diff --git a/cli/test/Makefile b/cli/test/Makefile
new file mode 100644
index 000000000..5846cdff6
--- /dev/null
+++ b/cli/test/Makefile
@@ -0,0 +1,28 @@
+# Note that these actually #include everything they need, except ccan/ and bitcoin/.
+# That allows for unit testing of statics, and special effects.
+CLI_TEST_SRC := $(wildcard cli/test/run-*.c)
+CLI_TEST_OBJS := $(CLI_TEST_SRC:.c=.o)
+CLI_TEST_PROGRAMS := $(CLI_TEST_OBJS:.o=)
+
+ALL_TEST_PROGRAMS += $(CLI_TEST_PROGRAMS)
+ALL_OBJS += $(CLI_TEST_OBJS)
+
+CLI_TEST_COMMON_OBJS :=				\
+	common/configdir.o			\
+	common/daemon_conn.o			\
+	common/htlc_state.o			\
+	common/json.o				\
+	common/pseudorand.o			\
+	common/memleak.o			\
+	common/msg_queue.o			\
+	common/utils.o				\
+	common/type_to_string.o			\
+	common/permute_tx.o
+
+update-mocks: $(CLI_TEST_SRC:%=update-mocks/%)
+
+$(CLI_TEST_PROGRAMS): $(CCAN_OBJS) $(BITCOIN_OBJS) $(WIRE_OBJS) $(LIBBASE58_OBJS) $(CLI_TEST_COMMON_OBJS)
+
+$(CLI_TEST_OBJS): $(LIGHTNING_CLI_HEADERS) $(LIGHTNING_CLI_SRC)
+
+check: $(CLI_TEST_PROGRAMS:%=unittest/%)
diff --git a/cli/test/run-large-input.c b/cli/test/run-large-input.c
new file mode 100644
index 000000000..a9d81810f
--- /dev/null
+++ b/cli/test/run-large-input.c
@@ -0,0 +1,116 @@
+#include <assert.h>
+#include <fcntl.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+int test_main(int argc, char *argv[]);
+ssize_t test_read(int fd, void *buf, size_t len);
+int test_socket(int domain, int type, int protocol);
+int test_connect(int sockfd, const struct sockaddr *addr,
+		 socklen_t addrlen);
+int test_getpid(void);
+int test_printf(const char *format, ...);
+
+#define main test_main
+#define read test_read
+#define socket test_socket
+#define connect test_connect
+#define getpid test_getpid
+#define printf test_printf
+
+  #include "../lightning-cli.c"
+#undef main
+
+/* AUTOGENERATED MOCKS START */
+/* Generated stub for version_and_exit */
+char *version_and_exit(const void *unused UNNEEDED)
+{ fprintf(stderr, "version_and_exit called!\n"); abort(); }
+/* AUTOGENERATED MOCKS END */
+
+int test_socket(int domain, int type, int protocol)
+{
+	/* We give a real fd, as it writes to it */
+	return open("/dev/null", O_WRONLY);
+}
+
+int test_connect(int sockfd, const struct sockaddr *addr,
+		 socklen_t addrlen)
+{
+	return 0;
+}
+
+int test_getpid(void)
+{
+	return 9999;
+}
+
+int test_printf(const char *fmt, ...)
+{
+	return 0;
+}
+
+static char *response;
+static size_t response_off, max_read_return;
+
+ssize_t test_read(int fd, void *buf, size_t len)
+{
+	if (len > max_read_return)
+		len = max_read_return;
+	if (len > strlen(response + response_off))
+		len = strlen(response + response_off);
+
+	memcpy(buf, response + response_off, len);
+	response_off += len;
+	return len;
+}
+
+/* Simulate a real log file I captured */
+#define NUM_ENTRIES (137772/2)
+
+#define HEADER "{ \"jsonrpc\": \"2.0\",\n"				\
+	       "    \"id\": \"lightning-cli-9999\",\n"			\
+	       "    \"result\" : {\n"					\
+	       "        \"creation_time\" : \"1515999039.806099043\",\n" \
+	       "        \"bytes_used\" : 10787759,\n"			\
+	       "        \"bytes_max\" : 20971520,\n"			\
+	       "        \"log\" : [\n"
+#define LOG_ENTRY							\
+	"            {\"type\": \"SKIPPED\", \"num_skipped\": 22},\n"	\
+	"            {\"type\": \"DEBUG\", \"time\": \"241693.051558854\", \"source\": \"lightning_gossipd(14581):\", \"log\": \"TRACE: nonlocal_gossip_broadcast_done\"},\n"
+#define TAILER	"] } }"
+
+int main(int argc, char *argv[])
+{
+	char *fake_argv[] = { argv[0], "--lightning-dir=/tmp/", "test", NULL };
+
+
+	/* sizeof() is an overestimate, but we don't care. */
+	response = tal_arr(NULL, char,
+			   sizeof(HEADER)
+			   + sizeof(LOG_ENTRY) * NUM_ENTRIES
+			   + sizeof(TAILER));
+
+	strcpy(response, HEADER);
+	response_off = strlen(HEADER);
+
+	/* Append a huge log */
+	for (size_t i = 0; i < NUM_ENTRIES; i++) {
+		memcpy(response + response_off, LOG_ENTRY, sizeof(LOG_ENTRY)-1);
+		response_off += sizeof(LOG_ENTRY)-1;
+	}
+
+	memcpy(response + response_off, TAILER, sizeof(TAILER)-1);
+	response_off += sizeof(TAILER)-1;
+	response[response_off++] = '\0';
+	assert(strlen(response) == response_off - 1);
+	assert(response_off < tal_len(response));
+
+	response_off = 0;
+	max_read_return = -1;
+	assert(test_main(3, fake_argv) == 0);
+	tal_free(response);
+	return 0;
+}