Sample Code:

//Create Document
ContentVersion cv = new ContentVersion();
cv.Title = 'Test Document';
cv.PathOnClient = 'TestDocument.pdf';
cv.VersionData = Blob.valueOf('Test Content');
cv.IsMajorVersion = true;
Insert cv;

//Get Content Version
List<ContentVersion> cvList = [SELECT Id, Title, ContentDocumentId FROM ContentVersion WHERE Id = :cv.Id];
System.assertEquals(cvList.size(), 1);

//Get Content Documents
List<ContentDocument> cdList = [SELECT Id, Title, LatestPublishedVersionId FROM ContentDocument];
System.assertEquals(cdList.size(), 1);