Should have used a proper mock

test_kv_store_protocol_handlers.cpp

// This is an example unit test for a function `kv_store_write_protocol_cmd`
//
// The purpose is to show that `kv_store_write` should have been implemented
// as a mock using a mocking framework, rather than a roll-your-own mock.

#include "CppUTest/TestHarness.h"
#include "CppUTestExt/MockSupport.h"

extern "C" {
  #include <string.h>
  #include <stddef.h>

  #include "kv_store/kv_store_protocol_handlers.h"
  #include "kv_store/kv_store.h"
}

static char s_key_written[1024];
static uint8_t s_val_written[1024];
static uint32_t s_val_len;


// This is a hand-made mock, which should probably instead
// be written with a mock library
bool kv_store_write(
    const char *key, 
    const void *val, 
    uint32_t len) {
  // Copy all data into buffers we can read later.
  strcpy(s_key_written, key, strlen(key));
  memcpy(s_val_written, val, len);
  s_val_len = len;
  return true;
}

TEST(TestKvStoreProtocolHandlers, Write) {
  // Key: "hello"
  // Val: "world"
  const uint8_t in_bytes[] = {
      'h', 'e', 'l', 'l', 'o', '\0', // Key
      'w', 'o', 'r', 'l', 'd'        // Value
  };

  const uint8_t kv_val_bytes[] = {
      'w', 'o', 'r', 'l', 'd'
  };

  // This calls kv_store_write
  kv_store_write_protocol_cmd(
      in_bytes, sizeof(in_bytes), 
      s_resp_buffer, &s_resp_buffer_len);

  STRCMP_EQUAL("hello", s_key_written,);
  MEMCMP_EQUAL(kv_val_bytes, s_val_written, sizeof(kv_val_bytes));
  LONGS_EQUAL(sizeof(kv_val_bytes), s_val_len);
}