如何在 Ruby 中对类实例的相同性/相等性进行单元测试？

Question

我正在尝试对 Ruby 中一个类的两个实例的相同性进行单元测试：

def test_example
    a = Object.new
    b = Object.new

    assert_equal a, b
end

我知道这会失败，因为实例是不同的变量，每个变量都有自己的内存指针。我所追求的是如果实例在所有方面都相同但它们的引用指针相同，则通过此测试。

这是一个更复杂（如果是人为的话）的例子：

# Let's stir up something...
class FooBar
    attr_accessor :seed, :foo, :bar

    def foo_the_bar()
        @bar = @seed + @foo * 3
    end
end

f = FooBar.new
f.seed = "Mountains "
f.foo  = "are just mountains "
f.bar = "obliterate me!"
f.foo_the_bar
p f.bar # "Mountains are just mountains are just mountains are just mountains "


# So far so good, now let's test if one FooBar is same as another...

require 'test/unit'
class FooBarTest < Test::Unit::TestCase

    # Test fails: <#<FooBar:0x9a40d18>> expected but was <#<FooBar:0x9a40d04>>.
    # But what we really want is a way to make this pass
    # since the objects are exactly the same in every respect,
    # besides their pointers.
    def test_foobar_1_init
        f1 = FooBar.new
        f2 = FooBar.new

        assert_equal f1, f2
    end

    # Again, test fails, but we want it to pass,
    # since the instance variables are the same.
    def test_foobar_2_instance_var
        f1 = FooBar.new
        f2 = FooBar.new

        f1.seed = "Santa says "
        f1.foo = "ho "
        f1.bar = "something"
        f1.foo_the_bar

        f2.seed = f1.seed
        f2.foo = f1.foo
        f2.foo_the_bar

        assert_equal f1, f2
    end

    # This test fails for the wrong reason.
    # We want this to fail because the instance variables are different.
    # This test should also fail if we add a method to one of the instances,
    # or make the instances differ from each some other way.
    def test_foobar_3_diff
        f1 = FooBar.new
        f2 = FooBar.new

        f1.seed = "Kitty goes "
        f1.foo = "meow "
        f1.foo_the_bar

        f2.seed = "Doggies goes "
        f2.foo = "woof "
        f2.foo_the_bar

        assert_equal f1, f2
    end
end

Answer 1

f1.attributes.keys.collect(&:to_sym).each do |field|
 assert_equal f1.send(field), f2.send(field)
end

这将断言所有字段的相等性。但缺点是断言的数量。如果您不希望这种情况发生，请像这样为对象分配 id

f1.id = 1
f2.id = 1 
assert_equal f1, f2

但请务必不要保存可能导致不一致的对象。

Answer 2

只需定义FooBar#==方法：

class FooBar
  def ==(other)
    [bar, seed, foo] == [other.bar, other.seed, other.foo]
  end
end

现在 test_foobar_1_init 和 test_foobar_2_instance_var 通过，test_foobar_3_diff 因正确原因而失败。

缺点是当你改变对象结构时，== 方法需要做相应的修改。

Answer 3

根据apidock 的来源，assert_equals 首先使用inspect 方法将对象转换为字符串。您应该为 class FooBar 定义检查方法

class FooBar
  def inspect
    # create a unique string of attributes here, maybe a json string.
  end
end