diff --git a/Makefile b/Makefile
index b9482e4..eb3f4d6 100644
--- a/Makefile
+++ b/Makefile
@@ -5,14 +5,15 @@ LDLIBS = -lm
 Sources = src/sieve_of_eratosthenes.c src/sieve_of_atkin.c
 Objects = $(Sources:.c=.o)
 
-.PHONY: sieve bench
+.PHONY: all
 
-sieve: target/sieve
+all: target/sieve target/bench target/tests
 
 target/sieve: $(Objects) src/main.c
 	$(LINK.c) $^ -o $@ $(LDLIBS)
 
-bench: target/bench
-
 target/bench: $(Objects) bench/bench.cc
 	$(LINK.cc) $^ -o $@ $(LDLIBS)
+
+target/tests: $(Objects) tests/tests.c
+	$(LINK.c) $^ -o $@ $(LDLIBS)
diff --git a/autoformat.bash b/autoformat.bash
index 0a22123..7fffd44 100755
--- a/autoformat.bash
+++ b/autoformat.bash
@@ -1,6 +1,6 @@
 #! /usr/bin/env bash
 
-files=(src/*.c*)
+files=(*/*.c*)
 if [ "$1" = check ]
 then
     clang-format --dry-run -Werror ${files[@]}
diff --git a/tests/tests.c b/tests/tests.c
new file mode 100644
index 0000000..d81094e
--- /dev/null
+++ b/tests/tests.c
@@ -0,0 +1,26 @@
+#include <assert.h>
+#include <stddef.h>
+
+struct SieveOfEratosthenes;
+struct SieveOfEratosthenes *sieve_of_eratosthenes_new(size_t limit);
+size_t sieve_of_eratosthenes_count(struct SieveOfEratosthenes *erato);
+void sieve_of_eratosthenes_delete(struct SieveOfEratosthenes *erato);
+
+struct SieveOfAtkin;
+struct SieveOfAtkin *sieve_of_atkin_new(size_t limit);
+size_t sieve_of_atkin_count(struct SieveOfAtkin *atkin);
+void sieve_of_atkin_delete(struct SieveOfAtkin *atkin);
+
+int
+main(void)
+{
+    struct SieveOfEratosthenes *erato = sieve_of_eratosthenes_new(1000000000);
+    size_t erato_count = sieve_of_eratosthenes_count(erato);
+    sieve_of_eratosthenes_delete(erato);
+    assert(erato_count == 50847531);
+
+    struct SieveOfAtkin *atkin = sieve_of_atkin_new(1000000000);
+    size_t atkin_count = sieve_of_atkin_count(atkin);
+    sieve_of_eratosthenes_delete(erato);
+    assert(atkin_count == 50847531);
+}