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                namespace Tests\Wikibase\DataModel\Deserializers;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Deserializers\Deserializer;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Wikibase\DataModel\Deserializers\AliasGroupListDeserializer;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Wikibase\DataModel\Term\AliasGroup;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                use Wikibase\DataModel\Term\AliasGroupList;  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                /**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @covers Wikibase\DataModel\Deserializers\AliasGroupListDeserializer  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 *  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @licence GNU GPL v2+  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @author Addshore  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 * @author Bene* < [email protected] >  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                 */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                class AliasGroupListDeserializerTest extends DeserializerBaseTest { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	/**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	 * @return Deserializer  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	 */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	public function buildDeserializer() { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                		return new AliasGroupListDeserializer();  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	}  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	public function deserializableProvider() { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                		return array( array() );  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	}  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	/**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	 * @return array[] things that aren't deserialized by the deserializer  | 
            
            
                                                                                                            
                                                                
            
                                    
            
            
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                	 */  | 
            
            
                                                                        
                            
            
                                    
            
            
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                	public function nonDeserializableProvider() { | 
            
            
                                                                        
                            
            
                                    
            
            
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                		return array(  | 
            
                            
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                			'must be an array' => array( new \stdClass() ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			'must be an array of arrays' => array( array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'en' => new \stdClass(),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			'array key must match' => array( array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'en' => array( array( 'language' => 'de', 'value' => 'Evil language' ) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			'must be an array of arrays of arrays' => array( array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'en' => array( 'A' ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'de' => array( 'B' ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			'must contain language' => array( array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'en' => array( array( 'value' => 'foo' ) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			'must contain value' => array( array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'en' => array( array( 'language' => 'en' ) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			'must not contain source' => array( array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				'en' => array(  | 
            
            
                                                                        
                            
            
                                    
            
            
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                					array( 'language' => 'en', 'value' => 'Evil language', 'source' => 'fallback' ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                				),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                			) ),  | 
            
            
                                                                        
                            
            
                                    
            
            
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                		);  | 
            
            
                                                                        
                            
            
                                    
            
            
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                	}  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	/**  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	 * @return array[] an array of array( object deserialized, serialization )  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	 */  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	public function deserializationProvider() { | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                		return array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                			array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				new AliasGroupList( array( new AliasGroup( 'en', array() ) ) ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				array( 'en' => array() ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                			),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                			array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				new AliasGroupList( array( new AliasGroup( 'en', array( 'A' ) ) ) ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				array( 'en' => array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                					array( 'language' => 'en', 'value' => 'A' ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				) ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                			),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                			array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				new AliasGroupList( array( new AliasGroup( 'en', array( 'A', 'B' ) ) ) ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				array( 'en' => array(  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                					array( 'language' => 'en', 'value' => 'A' ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                					array( 'language' => 'en', 'value' => 'B' ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                				) ),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                			),  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                		);  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                	}  | 
            
            
                                                                                                            
                            
            
                                    
            
            
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                }  | 
            
            
                                                        
            
                                    
            
            
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If you return a value from a function or method, it should be a sub-type of the type that is given by the parent type f.e. an interface, or abstract method. This is more formally defined by the Lizkov substitution principle, and guarantees that classes that depend on the parent type can use any instance of a child type interchangably. This principle also belongs to the SOLID principles for object oriented design.
Let’s take a look at an example:
Our function
my_functionexpects aPostobject, and outputs the author of the post. The base classPostreturns a simple string and outputting a simple string will work just fine. However, the child classBlogPostwhich is a sub-type ofPostinstead decided to return anobject, and is therefore violating the SOLID principles. If aBlogPostwere passed tomy_function, PHP would not complain, but ultimately fail when executing thestrtouppercall in its body.