google 假的模拟委托必须是可复制构造的

Question

使用 google 测试和模拟，如果函数 return 是对数据对象的引用，我似乎无法将调用从模拟委托给伪造。我使用的 google 测试版本是发布的 zip 中的 1.10.0。

在下面的代码中，当我从一个 mock 委托给一个 fake 时，我收到一条错误消息，指出复制 ctor 已被删除。是的，必须删除它才能使此代码正常工作。

对于 return 引用 classes 的函数，是否有任何方法可以使用 gmock 将模拟委托给伪造？

请注意，在下面的代码中，有一个宏： #define USE_MOCK_ACCESSOR 1 这用于测试测试代码执行的所需路径。将此值定义为零仅测试 AccessorImpl class 的正确行为。我这样做是为了检查我没有以某种方式使 class 中的 classes 和实例变形。感谢您的输入。

#include "gtest/gtest.h"
#include "gmock/gmock.h"

#include <cstdint>

using ::testing::Invoke;
using ::testing::Mock;
using ::testing::Return;
using ::testing::ReturnRef;
using ::testing::_;

class Accessor
{
public:
    virtual ~Accessor()                  = default;
    Accessor()                           = default;
    Accessor(Accessor const&)            = delete;
    Accessor(Accessor&&)                 = delete;
    Accessor& operator=(Accessor const&) = delete;
    Accessor& operator=(Accessor&&)      = delete;

    struct Foo
    {
        ~Foo()                     = default;
        Foo()                      = default;
        Foo(Foo const&)            = delete;
        Foo(Foo&&)                 = delete;
        Foo& operator=(Foo const&) = delete;
        Foo& operator=(Foo&&)      = delete;

        uint32_t thing_1 = 13u;
    };

    struct Bar
    {
        ~Bar()                     = default;
        Bar()                      = default;
        Bar(Bar const&)            = delete;
        Bar(Bar&&)                 = delete;
        Bar& operator=(Bar const&) = delete;
        Bar& operator=(Bar&&)      = delete;

        uint32_t thing_2 = 79u;
    };

    virtual Foo&       GetFoo()       = 0;
    virtual Bar const& GetBar() const = 0;
};

class AccessorImpl: public Accessor
{
public:
    ~AccessorImpl() override                       = default;
    AccessorImpl()                                 = default;
    AccessorImpl(AccessorImpl const& ) = delete;
    AccessorImpl(AccessorImpl&&)                   = delete;
    AccessorImpl& operator=(AccessorImpl const&)   = delete;
    AccessorImpl& operator=(AccessorImpl&&)        = delete;

    Foo&       GetFoo()       override { return this->foo_; };
    Bar const& GetBar() const override { return this->bar_; };

private:
    Foo foo_;
    Bar bar_;
};

#define USE_MOCK_ACCESSOR 1
#if USE_MOCK_ACCESSOR
class MockAccessor : public Accessor
{
public:
    MOCK_METHOD0(GetFoo, Foo&());
    MOCK_CONST_METHOD0(GetBar, Bar&());
};

class MockAccessorWithFake : public MockAccessor
{
public:
    MockAccessorWithFake() : MockAccessor(), fake_accessor_()
    {
        ON_CALL(*this, GetFoo).WillByDefault([this]() {
            return this->fake_accessor_.GetFoo();
        });

        ON_CALL(*this, GetBar).WillByDefault([this]() {
            return this->fake_accessor_.GetBar();
        });
    }

private:
    AccessorImpl fake_accessor_;
};
#endif

TEST(AccessorTest, test)
{
#if USE_MOCK_ACCESSOR
    MockAccessorWithFake accessor;
#else
    AccessorImpl accessor;
#endif
    EXPECT_EQ(accessor.GetFoo().thing_1, 13u);
    EXPECT_EQ(accessor.GetBar().thing_2, 79u);
}

来自 clang 编译器的错误：

test_accessor.cc:83:20: error: call to deleted constructor of 'Accessor::Foo'
            return this->fake_accessor_.GetFoo();
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

test_accessor.cc:26:9: note: 'Foo' has been explicitly marked deleted here
        Foo(Foo const&)            = delete;
        ^

test_accessor.cc:82:46: error: no viable conversion from '(lambda at
      test_accessor.cc:82:46)' to 'const Action<Accessor::Foo &()>'
        ON_CALL(*this, GetFoo).WillByDefault([this]() {
                                             ^~~~~~~~~~

googletest-src/googlemock/include/gmock/gmock-actions.h:339:7: note: candidate constructor (the implicit copy constructor) not viable:
      no known conversion from '(lambda at test_accessor.cc:82:46)' to 'const testing::Action<Accessor::Foo &()> &' for 1st argument
class Action {
      ^

googletest-src/googlemock/include/gmock/gmock-actions.h:339:7: note: candidate constructor (the implicit move constructor) not viable:
      no known conversion from '(lambda at test_accessor.cc:82:46)' to 'testing::Action<Accessor::Foo &()> &&' for 1st argument

googletest-src/googlemock/include/gmock/gmock-actions.h:367:3: note: candidate template ignored: requirement
      '::std::is_constructible<std::__1::function<Accessor::Foo &()>, (lambda at test_accessor.cc:82:46)>::value' was not satisfied
      [with G = (lambda at test_accessor.cc:82:46)]
  Action(G&& fun) : fun_(::std::forward<G>(fun)) {}  // NOLINT
  ^

googletest-src/googlemock/include/gmock/gmock-spec-builders.h:323:46: note: passing argument to parameter 'action' here
  OnCallSpec& WillByDefault(const Action<F>& action) {

Answer 1

问题 1

auto 类型扣除带引用的规则。因此，您的 lambda 的 return 类型被推断为 Foo 而不是 Foo& 然后需要一个副本。如果你想 return 来自 lambda 的引用，你必须使用尾随 return 类型语法明确指定，或者通过将 return 类型显式设置为 Foo&，通过使用 auto& 强制引用类型推导，或使用 decltype(auto) 来保留引用。见link, link, link，最后link相关部分是：“如果P是引用类型，则P所引用的类型用于推导。”

[this]() {return this->fake_accessor_.GetFoo();}          // Returns Foo
[this]() -> Foo& {return this->fake_accessor_.GetFoo();}  // Returns Foo&

[this]() -> auto {return this->fake_accessor_.GetFoo();}  // Returns Foo
[this]() -> auto& {return this->fake_accessor_.GetFoo();} // Returns Foo&

[this]() -> decltype(auto) {return this->fake_accessor_.GetFoo();} // Returns Foo&

因此您应该将传递给 ON_CALL 的 lambda 更改为 return 引用类型，例如：

        ON_CALL(*this, GetFoo).WillByDefault([this]() -> Foo& {
            return this->fake_accessor_.GetFoo();
        });

        ON_CALL(*this, GetBar).WillByDefault([this]() -> Bar const& {
            return this->fake_accessor_.GetBar();
        });

没有这个，你会得到错误：

test.cpp:83:20: error: call to deleted constructor of 'Accessor::Foo'
            return this->fake_accessor_.GetFoo();
                   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
test.cpp:26:9: note: 'Foo' has been explicitly marked deleted here
        Foo(Foo const&)            = delete;
        ^
test.cpp:82:46: error: no viable conversion from '(lambda at test.cpp:82:46)' to 'const Action<Accessor::Foo &()>'
        ON_CALL(*this, GetFoo).WillByDefault([this]() {
                                             ^~~~~~~~~~

问题 2

在 GetBar 的声明中，const 有两种用法：

该函数是一个const成员函数（意味着它不能修改this的状态）。
return 值是对 const Bar 的引用。

MOCK_CONST_METHOD0宏只声明了const成员函数。要覆盖 return 值中的 const，您的 mock 应该是：

  MOCK_CONST_METHOD0(GetBar, Bar const&());

如果不进行此更改，将生成以下错误：

test.cpp:86:46: error: no viable conversion from '(lambda at test.cpp:86:46)' to 'const Action<Accessor::Bar &()>'
        ON_CALL(*this, GetBar).WillByDefault([this]() -> Bar const& {
                                             ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/gmock/gmock-actions.h:357:7: note: candidate constructor (the implicit copy constructor) not viable: no known conversion from '(lambda at test.cpp:86:46)' to 'const testing::Action<Accessor::Bar &()> &' for 1st argument
class Action {

google 假的模拟委托必须是可复制构造的

google mock delegate to fake must be copy constructable

c++

googletest

googlemock

问题 1

问题 2