This is a test.  This is only a test.
This iThis is only a test.  s a test.  
This is a This is only a test.  test.  
TThis is only a test.  his is a test.  
ThThis is only a test.  is is a test.  
This is a teThis is only a test.  st.  
This is a tesThis is only a test.  t.  
This is a tThis is only a test.  est.  
ThiThis is only a test.  s is a test.  
This is This is only a test.  a test.  
This is only a test.  This is a test.  
This is not a test.  Be very afraid.