Update output parentheses in tests

Author: asterycs

test/StdTest.jl

@@ -343,12 +343,12 @@ end
     @test to_std_string(gradient(x' * sin(y) * a, x)) == "asin(y)"
     @test to_std_string(gradient(y' * sin(x) * a, x)) == "a(cos(x) ⊙ y)"
     @test to_std_string(gradient(sum(x), x)) == "vec(1)"
-    @test_broken to_std_string(gradient(2 * sum(x), x)) == "2(vec(1))"
-    @test_broken to_std_string(gradient(sum(2 * x), x)) == "2(vec(1))"
+    @test to_std_string(gradient(2 * sum(x), x)) == "2vec(1)"
+    @test to_std_string(gradient(sum(2 * x), x)) == "2vec(1)"
     @test to_std_string(gradient(sum(x .^ 2), x)) == "2x"
     @test to_std_string(gradient(sum(x .^ 3), x)) == "3x²"
     @test to_std_string(gradient(sum((x + y) .^ 2), x)) == "2(x + y)"
-    @test_broken to_std_string(gradient(sum((x .* y) .^ 2), x)) == "2(x ⊙ y ⊙ y)"
+    @test to_std_string(gradient(sum((x .* y) .^ 2), x)) == "2x ⊙ y ⊙ y"
     @test to_std_string(gradient(sum((A * x - y) .^ 2), x)) == "2Aᵀ(Ax - y)"
     @test to_std_string(gradient((x' * A * x) .^ (-2), x)) == "(-2)(xᵀAᵀx)⁻³(Aᵀx + Ax)"
     @test to_std_string(gradient(((A .* B) * C * x)' * x, x)) == "(A ⊙ B)Cx + Cᵀ(Aᵀ ⊙ Bᵀ)x"