text: 
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  #include <boost/test/unit_test.hpp>
  
  #include <stdlib.h>
  
  #include <rpc/blockchain.h>
  #include <test/test_bitcoin.h>
  
  /*双打之间的均等是不精确的。应进行比较
   *公差阈值较小，而不是完全相等。
   **/
  
  static bool DoubleEquals(double a, double b, double epsilon)
  {
      return std::abs(a - b) < epsilon;
  }
  
  static CBlockIndex* CreateBlockIndexWithNbits(uint32_t nbits)
  {
      CBlockIndex* block_index = new CBlockIndex();
      block_index->nHeight = 46367;
      block_index->nTime = 1269211443;
      block_index->nBits = nbits;
      return block_index;
  }
  
  static void RejectDifficultyMismatch(double difficulty, double expected_difficulty) {
       BOOST_CHECK_MESSAGE(
          DoubleEquals(difficulty, expected_difficulty, 0.00001),
          "Difficulty was " + std::to_string(difficulty)
              + " but was expected to be " + std::to_string(expected_difficulty));
  }
  
  /*给定一个具有所提供nbits的blockindex，
   *验证预期的困难结果。
   **/
  
  static void TestDifficulty(uint32_t nbits, double expected_difficulty)
  {
      CBlockIndex* block_index = CreateBlockIndexWithNbits(nbits);
      double difficulty = GetDifficulty(block_index);
      delete block_index;
  
      RejectDifficultyMismatch(difficulty, expected_difficulty);
  }
  
  BOOST_FIXTURE_TEST_SUITE(blockchain_tests, BasicTestingSetup)
  
  BOOST_AUTO_TEST_CASE(get_difficulty_for_very_low_target)
  {
      TestDifficulty(0x1f111111, 0.000001);
  }
  
  BOOST_AUTO_TEST_CASE(get_difficulty_for_low_target)
  {
      TestDifficulty(0x1ef88f6f, 0.000016);
  }
  
  BOOST_AUTO_TEST_CASE(get_difficulty_for_mid_target)
  {
      TestDifficulty(0x1df88f6f, 0.004023);
  }
  
  BOOST_AUTO_TEST_CASE(get_difficulty_for_high_target)
  {
      TestDifficulty(0x1cf88f6f, 1.029916);
  }
  
  BOOST_AUTO_TEST_CASE(get_difficulty_for_very_high_target)
  {
      TestDifficulty(0x12345678, 5913134931067755359633408.0);
  }
  
  BOOST_AUTO_TEST_SUITE_END()
  