$this->assertEquals( true, … ) is already reported as problematic by the sniff, because it would accept numeric values, but should only accept boolean true.

$this->assertEquals( 0, … ) and similar are also reported, because they would accept a wide variety of values that are all considered false in PHP.

What's currently not reported by the sniff are numeric values and strings that can be confused with true:

$this->assertEquals( 1, true );
$this->assertEquals( 1.0, true );
$this->assertEquals( '1', true );
$this->assertEquals( '1.0', true );
$this->assertEquals( '1.00', true );

Note that other numeric values (e.g. '2') are not considered equal to true, because what PHPUnit's ScalarComparator internally does is not simply an == comparison, but (string)$a == (string)$b if one side is a string, or a straight == otherwise.