rewrote the concat test to avoid flaky failures (apache#14049)

ran 10000 times with no failures

contrib/clojure-package/test/org/apache/clojure_mxnet/operator_test.clj

@@ -51,33 +51,16 @@
  (is (= out-grad grad))))))
 
 (deftest test-concat
- (let [shape-vecs [[2 2] [3 2]]
- x (sym/variable "x")
- y (sym/variable "y")
- out (sym/concat "conc" nil [x y] {:dim 0})
- arr (mapv #(ndarray/empty %) shape-vecs)
- arr-np (mapv #(ndarray/copy %) arr)
- arr-grad (map #(ndarray/empty %) shape-vecs)
- arg-names (sym/list-arguments out)
- grad-map (zipmap arg-names arr-grad)
- args (sym/list-arguments out)
- [arg-shapes out-shapes aux-shapes] (sym/infer-shape out (zipmap args shape-vecs))
- out-shape-vec (first out-shapes)
- out-grad (ndarray/empty out-shape-vec)
- exec1 (sym/bind out (context/default-context) arr grad-map)
- out1 (-> (executor/forward exec1)
+ (let [a (sym/variable "a")
+ b (sym/variable "b")
+ c (sym/concat "conc" nil [a b] {:dim 0})
+ exec (sym/bind c (context/default-context) {"a" (ndarray/array [1 2] [2 1])
+ "b" (ndarray/array [3 4] [2 1])})
+ output (-> (executor/forward exec)
  (executor/outputs)
- (first))
- ret (ndarray/concatenate arr)]
- (is (= out1 ret))
-
- ;;backward
- (ndarray/copy-to out1 out-grad)
- (ndarray/+= out-grad 1)
- (executor/backward exec1 out-grad)
- (let [grads arr-grad
- np-grads arr-np]
- (is (= grads (mapv #(ndarray/+ % 1) np-grads))))))
+ (first))]
+ (is (= [1.0 2.0 3.0 4.0] (ndarray/->vec output)))
+ (is (= [4 1] (ndarray/shape-vec output)))))
 
 (defn check-regression [model forward-fn backward-fn]
  (let [shape-vec [3 1]