new file mode 100644

@@ -0,0 +1,14 @@

+#ifndef GENERATOR_H_

+#define GENERATOR_H_

+

+#include <string>

+#include <functional>

+

+using generator = std::function<std::string()>;

+

+inline generator make_generator() {

+    return [] {return std::string("234567");};

+}

+

+#endif

+

new file mode 100644

@@ -0,0 +1,29 @@

+#include <algorithm>

+

+#include "generator.h"

+#include "test_util.h"

+

+int six_digits()  {

+   // given

+   generator generator = make_generator();

+

+  // when

+  auto actual = generator();

+

+

+  // then

+  check(actual.size() == 6, "size is wrong");

+  check(std::all_of(actual.begin(), actual.end(), [](char c){ return c >= '0' && c <= '9';}), "not just digits");

+  succeed();

+}

+

+

+int run_tests() {

+    test(six_digits);

+    succeed();

+}

+

+int main(int argc, char *argv[]) {

+    return !run_tests();

+}

+