I don't know how can I test my contentdocumentlink, in the log I got the information
>EXCEPTION_THROWN [18]|System.QueryException: Implementation restriction: ContentDocumentLink requires a filter by a single Id on ContentDocumentId or LinkedEntityId using the equals operator or multiple Id's using the IN operator.

but I think I only selected one record.

For the "Wrapper implements Comparable", how can I test it? I read a bit about the testclass for that, but its not clear for me.

**Main class**
```java
public class DokuBox_6 {
	
	public List<Wrapper> wrapperList {get; set;}
	public String currentRecordId {get; set;}
	
	public DokuBox_6() {
		currentRecordId = ApexPages.currentPage().getParameters().get('id');
		
		if(wrapperList == null) {
			wrapperList = new List<Wrapper>();
			
			for(Task a: [select Id, Subject, CreatedDate, Createdby.Name, RecordType.Name from Task where WhoId =: currentRecordId limit 10]) {
				wrapperList.add(new Wrapper(a, 'Task'));
			}
			for(Event b: [select Id, Subject, CreatedDate, Createdby.Name from Event where WhoId =: currentRecordId limit 10]) {
				wrapperList.add(new Wrapper(b, 'Event'));
			}
			for(ContentDocumentLink d: [SELECT Id, ContentDocumentId, ContentDocument.Title, ContentDocument.createdDate, ContentDocument.Createdby.Name, ContentDocument.FileExtension FROM ContentDocumentLink WHERE LinkedEntityId =: currentRecordId limit 10]) {
				wrapperList.add(new Wrapper(d, 'Note/File'));
			}
			wrapperList.sort();
		}
	}
	
	public class Wrapper implements Comparable {
		
		private final String objectLabel;
		private final Id id;
		private final String subject;
		private final DateTime createDate;
		private final String Ersteller;
		private final String Typ;
		
		public wrapper(Task t, String oName) { 
			objectLabel 	= oName;
			id 				= t.Id;
			subject 		= t.Subject;
			createDate 		= t.CreatedDate;
			Ersteller 		= t.CreatedBy.Name;
			Typ				= t.RecordType.Name;
		}
		
		public wrapper(Event e, String oName) {
			objectLabel 	= oName;
			id 				= e.Id;
			subject 		= e.Subject;
			createDate 		= e.CreatedDate;
			Ersteller 		= e.CreatedBy.Name;
		}
		
		public wrapper(ContentDocumentLink f, String oName) {
			objectLabel 	= oName;
			id 				= f.ContentDocumentId;
			subject 		= f.ContentDocument.Title;
			createDate 		= f.ContentDocument.CreatedDate;
			Ersteller 		= f.ContentDocument.CreatedBy.Name;
			Typ				= f.ContentDocument.FileExtension;
		}
		
		public Id getId() {
			return id;
		}
		
		public String getSubject() {
			return subject;
		}
		
		public String getTyp() {
			return Typ;
		}    
		
		public DateTime getCreatedDate() {
			return createDate;
		}
		
		public String getObjectLabel() {
			return objectLabel;
		}

		public String getErsteller() {
			return Ersteller;
		}
		
		public Integer compareTo(Object compareTo) {
			Wrapper compareToActivity = (Wrapper) compareTo;
			DateTime compareToCreateDate = compareToActivity.getCreatedDate();
			if (createDate > compareToCreateDate) {
				return -1;
			}
			if (createDate < compareToCreateDate) {
				return 1;
			}
			return 0;
		}
	}
	
}
```

**Test class**
```
@isTest
private class DokuBox_Test {
	
	static testMethod void testMethod1() {

		DateTime cur=System.now();
		
		Account acc = new Account(Name = 'Test Account');
		insert acc;
		
		Contact con = new Contact(Firstname = 'John', Lastname = 'Doe');
		insert con;
		
		Task tsk = new Task(
			Subject = 'Call', 
			ActivityDate = Date.today().addDays(-1), 
			Description = 'Test', 
			WhatId = acc.Id
		);
		insert tsk;
		
		Event evt = new Event(
			WhatId = acc.id,
			Subject = 'Strategy',
			StartDateTime = Date.newInstance(cur.year(), cur.month(), 1) + 1,
			EndDateTime = Date.newInstance(cur.year(), cur.month(), 1 + 1)
		);
		insert evt;
		
		ContentVersion conVer = new ContentVersion(
			Title = 'Penguins',
			PathOnClient = 'Penguins.docx',
			VersionData = Blob.valueOf('Test Content'),
			IsMajorVersion = true,
			Vertraulichkeitsstufe__c = 'Intern',
			Dokumentenklasse__c = 'Geschäftsbrief'
		);
		insert conVer;  
		
		ContentDocumentLink cdl = New ContentDocumentLink();
		cdl.LinkedEntityId = acc.id;
		cdl.ContentDocumentId = [SELECT ContentDocumentId FROM ContentVersion WHERE Id =: conVer.id].ContentDocumentId;
		cdl.shareType = 'I';
		insert cdl;
		
		DokuBox_6 D6 = new DokuBox_6();

	}
}
```