Additional tests

[kostyfisik]

There is also a number of stupid tests which should be easily passed with the correct code, e.g.: several layers with the same index should give the same result for the same outer size, adding one more outer layer with air index should not change the result, tangential field components to the left and to the right of the border between layer should be the same, if we decrease some layer thickness to zero (or to almost zero) the changes of the index value of this layer should not change the result and so on...