Testing for deep equality with json marshaling in golang

Question

Given these two test cases:

func TestEqualWhat(t *testing.T) { testMarshalUnmarshal(t, map[string]interface{}{"a":"b"}) testMarshalUnmarshal(t, map[string]interface{}{"a":5}) }

Where the testMarshalUnmarshal helper just marshals to json and back out:

func testMarshalUnmarshal(t *testing.T, in map[string]interface{}) { //marshal the object to a string jsb, err := json.Marshal(in); if err != nil { log.Printf("Unable to marshal msg") t.FailNow() } //unmarshal to a map res := make(map[string]interface{}) if err := json.Unmarshal(jsb, &res); err != nil { t.FailNow() } if !reflect.DeepEqual(in, res) { log.Printf("\nExpected %#v\nbut got %#v", in, res) t.FailNow() } }

Why does the first test case pass and the second fail? The output of the test is this:

Expected map[string]interface {}{"a":5} but got map[string]interface {}{"a":5} --- FAIL: TestEqualWhat (0.00 seconds)

Here is similar code on the go playground so you can have a hack at it easily.

llimllib · Accepted Answer · 2013-06-25 19:45:07Z

I figured it out! JSON only has one numerical type, which is floating point, so all integers are converted to Float64 in the marshal/unmarshal process. So, in the res map, the 5 is a float64 instead of an int.

Here is a go playground that provides context and evidence of what I'm talking about.

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