Having two cases in a switch statement or two branches in an if chain with the same implementation is at best duplicate code, and at worst a coding error. If the same logic is truly needed for both instances, then in an if chain they should be combined, or for a switch, one should fall through to the other.

Noncompliant Code Example

switch ($i) {
  case 1:
    doFirst();
    doSomething();
    break;
  case 2:
    doSomethingDifferent();
    break;
  case 3:  // Noncompliant; duplicates case 1's implementation
    doFirst();
    doSomething();
    break;
  default:
    doTheRest();
}

if ($a >= 0 && $a < 10) {
  doFirst();
  doTheThing();
}
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doFirst();
  doTheThing();  // Noncompliant; duplicates first condition
}

Exceptions

Blocks in an if chain that contain a single line of code are ignored, as are blocks in a switch statement that contain a single line of code with or without a following break.

if ($a >= 0 && $a < 10) {
  doTheThing();
}
else if ($a >= 10 && $a < 20) {
  doTheOtherThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThing();  // no issue, usually this is done on purpose to increase the readability
}

But this exception does not apply to if chains without else-s, or to switch-es without default clauses when all branches have the same single line of code. In case of if chains with else-s, or of switch-es with default clauses, rule {rule:php:S3923} raises a bug.

if ($a >= 0 && $a < 10) {
  doTheThing();
}
else if ($a >= 20 && $a < 50) {
  doTheThing();   //Noncompliant; this might have been done on purpose but probably not
}