Add function for supporting JSON equality checks using byte slices

[GCrispino]

Summary

This PR adds a new function into the assert package, JSONEqBytes, that does the same as JSONEq, but by receiving []byte values as parameter instead of string ones.

Changes

assert/assertions.go: The implementation of JSONEqBytes is pretty much what was in JSONEq, but having it receive []byte values and then not needing to convert these values to []byte when calling json.Unmarshal inside it.

Then, the implementation of JSONEq was changed such that it just calls JSONEqBytes by converting its original arguments to []byte values (which it already did when calling json.Unmarshal)

assert/assertions_test.go: Tests for JSONEqBytes function were replicated from the tests from JSONEq.

Motivation

It is common in Go to store JSON text in []byte variables instead of string values, so having a function that allows to receive these values when doing JSON-equality checks without having to cast them to string can be useful.

Maybe not as important, it would also avoid unnecessary []byte-to-string conversions, which could add up when dealing with big JSON payloads.

Example of usage:

package main

import (
    "fmt"
    "testing"
    "github.com/stretchr/testify/assert"
    "github.com/stretchr/testify/require"
)


func TestJSONFiles(t *testing.T) {
    actualFile := "/path/to/file.json"
    byteValue, err := ioutil.ReadAll(jsonFile)
    require.NoError(t, err)

    expectedContentsFile := "/path/to/expected.json"
    byteValue, err = ioutil.ReadAll(jsonFile)
    require.NoError(t, err)

    assert.JSONEqBytes(t, expected, byteValue)
}

[hendrywiranto]

Hi ! this one is great but I think currently maintainers are more focused in fixing bugs rather than expanding the API interface.
Let's wait their response