Ensure hash stability

Reviewed and added tests for the missing ones.

ReferenceList: exists
Statement: new
Reference: new
SnakList: exists

SnakObject
- DerivedPropertyValueSnakTest: exists
- PropertyNoValueSnakTest: exists
- PropertySomeValueSnakTest: exists
- PropertyValueSnakTest: exists

Bug: T253637

Author: toban

tests/unit/ReferenceTest.php

@@ -188,6 +188,11 @@ public function testReferenceDoesNotEqualReferenceWithDifferentSnakProperty() {
 		$this->assertFalse( $reference0->equals( $reference1 ) );
 	}
 
+	public function testReferenceHashStability() {
+		$reference = new Reference( [ new PropertyNoValueSnak( 42 ) ] );
+		$this->assertSame( 'f2be45ba65676e69367433547812db03b8c661ef', $reference->getHash() );
+	}
+
 	public function testReferenceDoesNotEqualReferenceWithMoreSnaks() {
 		$reference0 = new Reference( [ new PropertyNoValueSnak( 42 ) ] );
 

tests/unit/Statement/StatementTest.php

@@ -79,6 +79,12 @@ public function testGetGuid( Statement $statement ) {
 		$this->assertEquals( 'foobar', $statement->getGuid() );
 	}
 
+	public function testHashStability() {
+		$mainSnak = new PropertyNoValueSnak( new PropertyId( 'P42' ) );
+		$statement = new Statement( $mainSnak );
+		$this->assertSame( '50c73da6759fd31868fb0cc9c218969fa776f62c', $statement->getHash() );
+	}
+
 	public function testSetAndGetMainSnak() {
 		$mainSnak = new PropertyNoValueSnak( new PropertyId( 'P42' ) );
 		$statement = new Statement( $mainSnak );