Add simple test from README.md

Makefile

@@ -1,17 +1,31 @@
 PREFIX = /usr/local
-CFLAGS += -Wall -Werror -std=c99 -c -D_GNU_SOURCE
+CFLAGS += -Wall -Werror -std=c99 -D_GNU_SOURCE
 
 .PHONY:
-	all clean install uninstall
+	all clean install uninstall test
 
-all:
-	$(CC) $(CFLAGS) src/flingfd.c -o src/.flingfd.o
-	$(AR) -rc libflingfd.a src/.flingfd.o
+all: libflingfd.a test-sender test-receiver
+
+%.o: %.c
+	$(CC) $(CFLAGS) -c $< -o $@
+
+libflingfd.a: src/flingfd.o
+	$(AR) -rc $@ $^
+
+test-sender: test.c src/flingfd.c
+	$(CC) $(CFLAGS) -DSENDER $^ -o $@
+
+test-receiver: test.c src/flingfd.c
+	$(CC) $(CFLAGS) $^ -o $@
+
+test: test-sender test-receiver
+	./test-sender & </dev/null; MYPID=$$! && \
+    ./test-receiver | grep -q "$$MYPID"
 
 clean:
-	rm -f libflingfd.a src/.flingfd.o
+	rm -f libflingfd.a src/flingfd.o test-receiver test-sender
 
-install: all
+install: libflingfd.a
 	cp src/flingfd.h $(PREFIX)/include
 	cp libflingfd.a $(PREFIX)/lib
 

test.c

@@ -0,0 +1,28 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <flingfd.h>
+
+char buf[32];
+
+void send_my_stdout() {
+    int fd = fileno(stdout);
+    flingfd_simple_send("/tmp/some_unique_path", fd);
+}
+
+void write_to_their_stdout() {
+    int fd = flingfd_simple_recv("/tmp/some_unique_path");
+    int n = snprintf(buf,32,"Hello world from %d\n", getpid());
+    write(fd, buf, n+1);
+}
+
+int main() {
+#ifdef SENDER
+    printf("Hello, I'm the sender My pid: %d\n", getpid());
+    write_to_their_stdout();
+#else
+    printf("Hello, I'm receiver. My pid: %d\n", getpid());
+    send_my_stdout();
+#endif
+    return 0;
+}