How to check whether the access of certain objects or schema as a specific user is valid?

Problem: How to check whether the access of certain objects or schema as a specific user is valid?

Solution:  EXECUTE AS

Sets the execution context of a session.

By default, a session starts when a user logs in and ends when the user logs off. All operations during a session are subject to permission checks against that user. When an EXECUTE AS statement is run, the execution context of the session is switched to the specified login or user name. After the context switch, permissions are checked against the login and user security tokens for that account instead of the person calling the EXECUTE AS statement. The user or login account is impersonated for the duration of the session or module execution, or the context switch is explicitly reverted.

Syntax:

{ EXEC | EXECUTE } AS <context_specification> 

[;] 

<context_specification>::= 

{ LOGIN | USER } = 'name' 

    [ WITH { NO REVERT | COOKIE INTO @varbinary_variable } ]  

| CALLER 

Example:

In this example, I would like to show we can check whether a user can execute a procedure.

EXECUTE AS user = 'testuser'

EXECUTE [dbo].[SelectTableB]

REVERT

Results:

Example 2: In this example, I would like to show how we can create a procedure to execute as the user level permission

-- to execute procedure

CREATE PROCEDURE [dbo].[SelectTableB]

WITH EXECUTE AS CALLER

AS

BEGIN

Select * FROM dbo.TableB

END