diff --git a/src/test_string_util.cpp b/src/test_string_util.cpp
index 593a083..2cc372e 100644
--- a/src/test_string_util.cpp
+++ b/src/test_string_util.cpp
@@ -25,7 +25,7 @@
 #include "string_util.h"
 #include "test_util.h"
 
-int main(int argc, char *argv[])
+void test_trim()
 {
   ASSERT_EQUALS(std::string("1234"), trim("  1234  "));
   ASSERT_EQUALS(std::string("1234"), trim("1234  "));
@@ -49,6 +49,35 @@ int main(int argc, char *argv[])
   ASSERT_EQUALS(std::string("-9223372036854775808"), str(std::numeric_limits<int64_t>::min()));
   ASSERT_EQUALS(std::string("0"), str(std::numeric_limits<uint64_t>::min()));
   ASSERT_EQUALS(std::string("18446744073709551615"), str(std::numeric_limits<uint64_t>::max()));
+}
 
+void test_base64()
+{
+  size_t len;
+  ASSERT_STREQUALS(s3fs_base64(NULL, 0), NULL);
+  ASSERT_STREQUALS(reinterpret_cast<const char *>(s3fs_decode64(NULL, &len)), NULL);
+  ASSERT_STREQUALS(s3fs_base64(reinterpret_cast<const unsigned char *>(""), 0), NULL);
+  ASSERT_STREQUALS(reinterpret_cast<const char *>(s3fs_decode64("", &len)), NULL);
+
+  ASSERT_STREQUALS(s3fs_base64(reinterpret_cast<const unsigned char *>("1"), 1), "MQ==");
+  ASSERT_STREQUALS(reinterpret_cast<const char *>(s3fs_decode64("MQ==", &len)), "1");
+  ASSERT_EQUALS(len, static_cast<size_t>(1));
+  ASSERT_STREQUALS(s3fs_base64(reinterpret_cast<const unsigned char *>("12"), 2), "MTI=");
+  ASSERT_STREQUALS(reinterpret_cast<const char *>(s3fs_decode64("MTI=", &len)), "12");
+  ASSERT_EQUALS(len, static_cast<size_t>(2));
+  ASSERT_STREQUALS(s3fs_base64(reinterpret_cast<const unsigned char *>("123"), 3), "MTIz");
+  ASSERT_STREQUALS(reinterpret_cast<const char *>(s3fs_decode64("MTIz", &len)), "123");
+  ASSERT_EQUALS(len, static_cast<size_t>(3));
+  ASSERT_STREQUALS(s3fs_base64(reinterpret_cast<const unsigned char *>("1234"), 4), "MTIzNA==");
+  ASSERT_STREQUALS(reinterpret_cast<const char *>(s3fs_decode64("MTIzNA==", &len)), "1234");
+  ASSERT_EQUALS(len, static_cast<size_t>(4));
+
+  // TODO: invalid input
+}
+
+int main(int argc, char *argv[])
+{
+  test_trim();
+  test_base64();
   return 0;
 }
diff --git a/src/test_util.h b/src/test_util.h
index 2422bd0..7180375 100644
--- a/src/test_util.h
+++ b/src/test_util.h
@@ -29,6 +29,18 @@ template <typename T> void assert_equals(const T &x, const T &y, const char *fil
   }
 }
 
+void assert_strequals(const char *x, const char *y, const char *file, int line)
+{
+  if(x == NULL && y == NULL){
+    return;
+  } else if((x == NULL || y == NULL) || strcmp(x, y) != 0){
+    std::cerr << x << " != " << y << " at " << file << ":" << line << std::endl;
+    std::exit(1);
+  }
+}
+
 #define ASSERT_EQUALS(x, y) \
   assert_equals((x), (y), __FILE__, __LINE__)
 
+#define ASSERT_STREQUALS(x, y) \
+  assert_strequals((x), (y), __FILE__, __LINE__)