如何在Ruby中对类实例的相同/相等进行单元测试？

Question

我想在Ruby中一个类的两个实例的单元测试千篇一律：

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

    assert_equal a, b 
end 

我明白，这将失败，因为情况是不同的变量，每个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是它们的引用指针通过此测试通过。

下面是一个更复杂的（如果做作）例如：

# 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 

这将宣称所有领域的平等。但缺点是断言的数量。如果你不希望这样的事情发生，分配ID的对象这样

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

但一定不救可能导致不一致的对象。

Answer 2

根据在apidock处的来源，assert_equals首先使用inspect方法将对象转换为字符串。你应该定义的检查方法为class FooBar

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

Answer 3

只要定义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，test_foobar_3_diff失败了正当的理由。

不利的一面是当你改变对象结构时，==方法需要相应修改。