docs: fix example with base operations

Author: MilesCranmer

test/test_base_2.jl

@@ -9,10 +9,10 @@
 
     First, let's create a node to reference `feature=1` of our dataset:
     =#
-    using DynamicExpressions, Random
+    using DynamicExpressions, Random, Test
 
     x = Node{Float64}(; feature=1)
-    @test x isa Node{Float64}
+    @test x isa Node{Float64,2}
 
     # We can also create values, using `val`:
     const_1 = Node{Float64}(; val=1.0)