如何在Ruby中對類實例的相同/相等進行單元測試？

Question

我想在Ruby中一個類的兩個實例的單元測試千篇一律：

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

    assert_equal a, b 
end 

我明白，這將失敗，因爲情況是不同的變量，每個都有自己的內存指針。我所追求的是如果實例在所有方面都相同但是它們的引用指針通過此測試通過。

下面是一個更復雜的（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 

這將宣稱所有領域的平等。但缺點是斷言的數量。如果你不希望這樣的事情發生，分配ID的對象這樣

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

但一定不救可能導致不一致的對象。

Answer 2

根據在apidock處的來源，assert_equals首先使用inspect方法將對象轉換爲字符串。你應該定義的檢查方法爲class FooBar

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

Answer 3

只要定義FooBar#==方法：

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

現在test_foobar_1_init和test_foobar_2_instance_var通，test_foobar_3_diff失敗了正當的理由。

不利的一面是當你改變對象結構時，==方法需要相應修改。