Add tests

test/test_rulenode_operators.jl

@@ -15,4 +15,27 @@ end
         @test !isvariable(g₁, RuleNode(7, g₁), SomeDefinitions)
         @test isvariable(g₁, RuleNode(7, g₁))
     end
+
+    @testset "Create `RuleNode`s with `Hole`s for children" begin
+        g = @csgrammar begin
+            A = 1 | 2 | 3
+            B = A + A
+        end
+
+        r = rulenode_with_empty_children(4, g)
+
+        @test get_children(r)[1].domain == [1, 1, 1, 0]
+        @test get_children(r)[2].domain == [1, 1, 1, 0]
+    end
+
+    @testset "Create `UniformHole`s with `Hole`s for children" begin
+        g = @csgrammar begin
+            A = 1 | 2 | 3
+            B = (A + A) | (A - A)
+        end
+        h = uniform_hole_with_empty_children(BitVector([0, 0, 0, 1, 1]), g)
+
+        @test get_children(h)[1].domain == [1, 1, 1, 0, 0]
+        @test get_children(h)[2].domain == [1, 1, 1, 0, 0]
+    end
 end