Salesforce - ContentDocumentLink in test class

Account acct = new Account(Name='TEST_ACCT');
insert acct;

ContentVersion contentVersion = new ContentVersion(
  Title = 'Penguins',
  PathOnClient = 'Penguins.jpg',
  VersionData = Blob.valueOf('Test Content'),
  IsMajorVersion = true
);
insert contentVersion;    
List<ContentDocument> documents = [SELECT Id, Title, LatestPublishedVersionId FROM ContentDocument];

//create ContentDocumentLink  record 
ContentDocumentLink cdl = New ContentDocumentLink();
cdl.LinkedEntityId = acct.id;
cdl.ContentDocumentId = documents[0].Id;
cdl.shareType = 'V';
insert cdl;