Add test for solve_quadratic_equation with no solution (#21)

Author: vil02

.spec/math/solve_quadratic_equation_spec.lua

@@ -29,4 +29,7 @@ describe("Quadratic equation solving", function()
 		assert.equal(complex.new(0, 0), a ^ 2 + p * a + q)
 		assert.equal(complex.new(0, 0), b ^ 2 + p * b + q)
 	end)
+	it("handles the case with no real solutions", function()
+		assert.equal(solve_quadratic_equation(0, 1), nil)
+	end)
 end)