googletest：sample8分析

目录

googletest：sample1
googletest：sample2
googletest：sample3
googletest：sample4
googletest：sample5
googletest：sample6
googletest：sample7
googletest：sample8
googletest：sample9

待测文件

同sample6，都是prime_tables.h文件

PrimeTable类声明了素数表的一系列接口，包括
1）IsPrime：判断当前输入数n是否为素数；
2）GetNextPrime：找比输入数n大的下一个素数.

文件内容略.

测试文件

如果我们想引进一种新的、改进的PrimeTable实现，结合了PrecalcPrimeTable的速度和OnTheFlyPrimeTable的多功能特性，用于判断一个数是否素数、获取下一个素数. 在内部，实例化了PrecalcPrimeTable, OnTheFlyPrimeTable，在特定情况下只使用更适合的一个. 但在内存不足时，可以在不实例化PreCalculatedPrimeTable的情况下实例化HybridPrimeTable，并且只使用OnTheFlyPrimeTable.

sample8_unittest.cc

// Suppose we want to introduce a new, improved implementation of PrimeTable
// which combines speed of PrecalcPrimeTable and versatility of
// OnTheFlyPrimeTable (see prime_tables.h). Inside it instantiates both
// PrecalcPrimeTable and OnTheFlyPrimeTable and uses the one that is more
// appropriate under the circumstances. But in low memory conditions, it can be
// told to instantiate without PrecalcPrimeTable instance at all and use only
// OnTheFlyPrimeTable.
class HybridPrimeTable : public PrimeTable {
 public:
  HybridPrimeTable(bool force_on_the_fly, int max_precalculated)
      : on_the_fly_impl_(new OnTheFlyPrimeTable),
        precalc_impl_(force_on_the_fly
                          ? nullptr
                          : new PreCalculatedPrimeTable(max_precalculated)),
        max_precalculated_(max_precalculated) {}
  ~HybridPrimeTable() override {
    delete on_the_fly_impl_;
    delete precalc_impl_;
  }

  bool IsPrime(int n) const override {
    if (precalc_impl_ != nullptr && n < max_precalculated_)
      return precalc_impl_->IsPrime(n);
    else
      return on_the_fly_impl_->IsPrime(n);
  }

  int GetNextPrime(int p) const override {
    int next_prime = -1;
    if (precalc_impl_ != nullptr && p < max_precalculated_)
      next_prime = precalc_impl_->GetNextPrime(p);

    return next_prime != -1 ? next_prime : on_the_fly_impl_->GetNextPrime(p);
  }

 private:
  OnTheFlyPrimeTable* on_the_fly_impl_;
  PreCalculatedPrimeTable* precalc_impl_;
  int max_precalculated_;
};

using ::testing::Bool;
using ::testing::Combine;
using ::testing::TestWithParam;
using ::testing::Values;

// To test all code paths for HybridPrimeTable we must test it with numbers
// both within and outside PreCalculatedPrimeTable's capacity and also with
// PreCalculatedPrimeTable disabled. We do this by defining fixture which will
// accept different combinations of parameters for instantiating a
// HybridPrimeTable instance.
class PrimeTableTest : public TestWithParam< ::std::tuple<bool, int> > {
 protected:
  void SetUp() override {
    bool force_on_the_fly;
    int max_precalculated;
    std::tie(force_on_the_fly, max_precalculated) = GetParam();
    table_ = new HybridPrimeTable(force_on_the_fly, max_precalculated);
  }
  void TearDown() override {
    delete table_;
    table_ = nullptr;
  }
  HybridPrimeTable* table_;
};

通过testing::TestWithParam<>的模板参数，将是否需要强制使用OnTheFlyPrimeTable (bool)和PreCalculatedPrimeTable (int)表中最大数 传递给PrimeTableTest，进而决定如何实例化HybridPrimeTable.

如何设计test？

跟普通的TEST类似依然可以用HybridPrimeTable提供接口进行测试.
当然，还能在test body中，通过GetParam()获取由INSTANTIATE_TEST_SUITE_P实例化的test parameter.

TEST_P(PrimeTableTest, ReturnsFalseForNonPrimes) {
  // Inside the test body, you can refer to the test parameter by GetParam().
  // In this case, the test parameter is a PrimeTable interface pointer which
  // we can use directly.
  // Please note that you can also save it in the fixture's SetUp() method
  // or constructor and use saved copy in the tests.

  EXPECT_FALSE(table_->IsPrime(-5));
  EXPECT_FALSE(table_->IsPrime(0));
  EXPECT_FALSE(table_->IsPrime(1));
  EXPECT_FALSE(table_->IsPrime(4));
  EXPECT_FALSE(table_->IsPrime(6));
  EXPECT_FALSE(table_->IsPrime(100));
}

TEST_P(PrimeTableTest, ReturnsTrueForPrimes) {
  EXPECT_TRUE(table_->IsPrime(2));
  EXPECT_TRUE(table_->IsPrime(3));
  EXPECT_TRUE(table_->IsPrime(5));
  EXPECT_TRUE(table_->IsPrime(7));
  EXPECT_TRUE(table_->IsPrime(11));
  EXPECT_TRUE(table_->IsPrime(131));
}

TEST_P(PrimeTableTest, CanGetNextPrime) {
  EXPECT_EQ(2, table_->GetNextPrime(0));
  EXPECT_EQ(3, table_->GetNextPrime(2));
  EXPECT_EQ(5, table_->GetNextPrime(3));
  EXPECT_EQ(7, table_->GetNextPrime(5));
  EXPECT_EQ(11, table_->GetNextPrime(7));
  EXPECT_EQ(131, table_->GetNextPrime(128));
}

设计完test，还需要用宏INSTANTIATE_TEST_SUITE_P来实例化"value-parameterized tests"，GoogleTest才会针对每个实例进行test.

// In order to run value-parameterized tests, you need to instantiate them,
// or bind them to a list of values which will be used as test parameters.
// You can instantiate them in a different translation module, or even
// instantiate them several times.
//
// Here, we instantiate our tests with a list of parameters. We must combine
// all variations of the boolean flag suppressing PrecalcPrimeTable and some
// meaningful values for tests. We choose a small value (1), and a value that
// will put some of the tested numbers beyond the capability of the
// PrecalcPrimeTable instance and some inside it (10). Combine will produce all
// possible combinations.
INSTANTIATE_TEST_SUITE_P(MeaningfulTestParameters, PrimeTableTest,
                         Combine(Bool(), Values(1, 10)));

注意：这里INSTANTIATE_TEST_SUITE_P第三个参数Combine(Bool(), Values(1, 10))对应的是TestWithParam< ::std::tuple<bool, int> >的模板参数，而sample7对应传的参数是Values(&CreateOnTheFlyPrimeTable, &CreatePreCalculatedPrimeTable<1000>)，即工厂方法的函数地址. 而我们用GetParam()获取的，就是这里的第三个参数.