Use assertSame() instead of assertEquals() where possible

[mhujer]

Repost of sebastianbergmann/phpunit-documentation#494.

---

I noticed that the introductory documentation chapter uses assertEquals(). I suggest that it can be replaced with assertSame(), which is stricter a may prevent unexpected type conversion bugs.

What do you think?

If you think it is a good idea, I can prepare a PR.

[keradus]

big 👍

[sebastianbergmann]

Go for it.

[mhujer]

I started changing the documentation, but when I was testing the example output I ran into an issue with the array not being diffed when assertSame is used.

See the example from docs:

<?php
use PHPUnit\Framework\TestCase;

class ArrayDiffTest extends TestCase
{
    public function testEquality() {
        $this->assertEquals(
            [1, 2,  3, 4, 5, 6],
            [1, 2, 33, 4, 5, 6]
        );
    }
}

It outputs this, so you can easily tell what's the problem:

1) ArrayDiffTest::testEquality
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
     0 => 1
     1 => 2
-    2 => 3
+    2 => 33

But when the assertEquals() is replaced with assertSame(), the output is the following, which is pretty hard to digest.

2) ArrayDiffTest::testEquality2             
Failed asserting that Array &0 (            
    0 => 1                                  
    1 => 2                                  
    2 => 33                                 
    3 => 4                                  
    4 => 5                                  
    5 => 6                                  
) is identical to Array &0 (                
    0 => 1                                  
    1 => 2                                  
    2 => 3                                  
    3 => 4                                  
    4 => 5                                  
    5 => 6                                  
). 

There is already an issue describing this sebastianbergmann/phpunit#2169 (and the older one sebastianbergmann/phpunit#1252).

I will try to have a look at the diffing issue first, because it would be hard to persuade users to use a stricter assert, if it provides worse DX.

EDIT: PR with the fix: sebastianbergmann/phpunit#2976