Keep identical address change IDs

An address change record allows two changes:
- setting an address
- opting out of the donation receipt

Each of those actions takes an `AddressChangeId` and "rotates" the
current ID to the `previousIdentifier`. When doing both changes, the Id
should only be rotated once, to avoid `hasBeenUsed` returning the wrong
value and to be able to check in the frontend if the previous ID still
returns a (used) address changed record.

Author: gbirke

src/Domain/Model/AddressChange.php

@@ -120,8 +120,10 @@ public function hasBeenUsed(): bool {
 	}
 
 	private function markAsModified( AddressChangeId $newIdentifier ): void {
-		$this->previousIdentifier = $this->getCurrentIdentifier();
-		$this->identifier = $newIdentifier;
+		if ( !$this->getCurrentIdentifier()->equals( $newIdentifier ) ) {
+			$this->previousIdentifier = $this->getCurrentIdentifier();
+			$this->identifier = $newIdentifier;
+		}
 
 		$this->modifiedAt = new \DateTime();
 		$this->resetExportState();

tests/Unit/Domain/Model/AddressChangeTest.php

@@ -152,4 +152,15 @@ public function testAddressChangesWithOptOutAreUsed(): void {
 
 		$this->assertTrue( $addressChange->hasBeenUsed() );
 	}
+
+	public function testMultipleModificationsWithTheSameIdentifierKeepsIdentifiers(): void {
+		$addressChange = $this->newPersonAddressChange();
+		$initialIdentifier = $addressChange->getCurrentIdentifier();
+
+		$addressChange->performAddressChange( ValidAddress::newValidPersonalAddress(), $this->newIdentifier );
+		$addressChange->optOutOfDonationReceipt( $this->newIdentifier );
+
+		$this->assertEquals( $initialIdentifier, $addressChange->getPreviousIdentifier() );
+		$this->assertEquals( $this->newIdentifier, $addressChange->getCurrentIdentifier() );
+	}
 }