This will work for the data that you supplied.
However, it makes the assumption that there will only ever be 1 match.
UPDATE t2
SET Mfg = t1.CompanyName

You could always extend tSQLt by writing your own case-sensitive assertion.  It's just a stored proc.
Then you could call
EXEC tSQLt.AssertEqualsStringCS @expected, @actual;

Just for fun, lets add some calculations to the groups
DECLARE @TableDate TABLE (TrxDate date PRIMARY KEY CLUSTERED, Value int NOT NULL);
INSERT INTO @TableDate ( TrxDate, Value...