The best way to properly test that the correct components display and hide for each scenario is to reset the DOM after each test with the afterEach() method. The afterEach() method is a lifecycle hook that runs after each test, and can be used to perform cleanup tasks, such as removing the elements from the DOM, resetting the mocks, or clearing the caches. This ensures that each test runs in a clean and isolated environment, and does not affect the results of other tests. Creating a new describe block for each test will not help, as the describe block is used to group related tests, but it does not reset the DOM after each test. Creating a teardown block to reset the DOM after each test will not work, as there is no such block in Jest, and the developer should use the afterEach() method instead. Creating a new jsdom instance for each test will not work, as jsdom is a JavaScript implementation of the DOM and HTML standards, and it is not a part of Jest, but a dependency that Jest uses to provide a browser-like environment. The developer should use the document object provided by Jest to manipulate the DOM, and use the afterEach() method to reset it. Reference: [Testing Lightning Web Components], [Jest Documentation]

The transient keyword is a keyword that can be used to declare instance variables that are not part of the view state of a Visualforce page. The view state is the state of the page that is persisted on the server and transferred to the client. The view state can affect the performance and user experience of the page, as it can increase the page load time, the response time, and the bandwidth consumption. By using the transient keyword, the developer can mark the variables that are not needed for rendering the page or maintaining the state, such as temporary variables, constants, or cached data. This way, the developer can reduce the size of the view state and improve the performance of the page. Reference: [transient Keyword], [View State]

The two queries that are optimized for large data volumes are: SELECT Id FROM Account WHERE Name != '' AND Customer_Number__c = 'ValueA', and SELECT Id FROM Account WHERE Id IN :aListVariable. An optimized query for large data volumes is a query that filters the records based on an indexed field or a field that has high selectivity. An indexed field is a field that has an index created by the system or the user to speed up the query performance. A field has high selectivity if the filter value in the query matches a low percentage of the total number of records for that object. The Customer_Number__c and Id fields are indexed fields, as they are custom fields that are marked as External Id, which creates an index. The Name field is also an indexed field, except when it is used with the LIKE operator. The != operator and the IN operator are selective operators, as they filter the records based on exact or list values, which can improve the selectivity. The AND operator allows the query to combine multiple filters, which can also improve the selectivity. The query SELECT Id FROM Account WHERE Name LIKE '!-NULL' is not an optimized query for large data volumes, as the LIKE operator with a wildcard character (%) at the beginning of the filter value is not selective, and the Name field is not indexed when used with the LIKE operator. The query SELECT Id FROM Account WHERE Name != '' AND IsDeleted = false is not an optimized query for large data volumes, as the IsDeleted field is not an indexed field, and the false value is not a selective value, as it matches a high percentage of the records. Reference: [Working with Very Large SOQL Queries], [Custom Field Attributes]