add a test for nested matrix multiplication

Author: mateuszbaran

src/DiffTests.jl

@@ -113,10 +113,12 @@ end
 
 self_weighted_logit(x) = inv(1.0 + exp(-dot(x, x)))
 
+nested_array_mul(x) = sum(sum(x[1] * [[x[2], x[3]]]))
+
 const VECTOR_TO_NUMBER_FUNCS = (vec2num_1, vec2num_2,  vec2num_3, vec2num_4, vec2num_5,
                                 vec2num_6, vec2num_7, rosenbrock_1, rosenbrock_2,
                                 rosenbrock_3, rosenbrock_4, ackley, self_weighted_logit,
-                                first)
+                                nested_array_mul, first)
 
 ########################
 # f(x::Matrix)::Number #