require 'matrix'
describe :trace, shared: true do
it "returns the sum of diagonal elements in a square Matrix" do
Matrix[[7,6], [3,9]].trace.should == 16
end
it "returns the sum of diagonal elements in a rectangular Matrix" do
lambda{ Matrix[[1,2,3], [4,5,6]].trace}.should raise_error(Matrix::ErrDimensionMismatch)
end
end