tSQLt Testing SQL Server security permissions

Is there a way to test security permissions in tSQLt?

Currently I am trying to test an accounts security and the results return from tSQLt are not what I am expecting. I am expecting on error that the account does not have permissions, but it appears that the "test" is using my account permissions and succeeding.

EXEC tSQLt.NewTestClass @ClassName = N'TestSecurity'    -- nvarchar(max)
go

CREATE PROCEDURE TestSecurity.[test execute as security]
AS 
BEGIN
    EXECUTE AS USER = 'account3'
    SELECT *
    FROM dbo.User AS u
    REVERT
END 
GO 
CREATE PROCEDURE TestSecurity.[test security on WebUser]
AS 
BEGIN
    EXECUTE AS USER = 'account3'
    SELECT *
    FROM dbo.WebUser AS wu
    REVERT
END 
GO 

EXEC tSQLt.Run
    @TestName = N'TestSecurity'
    --,@TestResultFormatter = N''  -- nvarchar(max)

Results are two table results printed and 2 successful tests:

(1 row affected)  
+----------------------+ 
|Test Execution Summary|
+----------------------+   '
|No|Test Case Name                           |Dur(ms)|Result |
+--+-----------------------------------------+-------+-------+ 
|1 |[TestSecurity].[test execute as security]|    257|Success|
|2 |[TestSecurity].[test security on SecUser]|     27|Success|
----------------------------------------------------------------------------- 
Test Case Summary: 2 test case(s) executed, 2 succeeded, 0 failed, 0 errored.
-----------------------------------------------------------------------------

When is reality the dbo.User table should have failed and the WebUser table should succeed? I expect an error but I get results back?

The error I expect to get back should look like

 -- run
 EXECUTE AS USER = 'account3'   
 SELECT *   FROM dbo.WebUser AS wu

-- returns
Msg 229, Level 14, State 5, Line 4
The SELECT permission was denied on the object 'WebUser', database '...', schema '...'.

I understand I should add tSQLt.ExpectException, but it is not even throwing an exception there are results coming back. I was trying to figure out how it is executing right now and then add the tSQLt Exception check. There is no security to return results so I am confused.

Update 1 Executing

CREATE PROCEDURE TestSecurity.[test execute as security]
AS 
BEGIN
    EXECUTE AS USER = 'account3'
    -- EDIT
    SELECT *
    FROM sys.user_token AS ut

    SELECT *
    FROM dbo.User AS u
    REVERT
END 
GO

Returns

name                type        usage
account3            SQL USER    GRANT OR DENY
public              ROLE        GRANT OR DENY
db_securitycheck    ROLE        GRANT OR DENY
db_executor         ROLE        GRANT OR DENY
db_webexecutor      ROLE        GRANT OR DENY
dbo                 SQL USER    AUTHENTICATOR
db_owner            ROLE        AUTHENTICATOR

Which kinda of makes sense except db_owner which are my permissions not the account3 permissions.