diff --git a/ast-generator/src/build_fn_gen.rs b/ast-generator/src/build_fn_gen.rs
index ab5f2e7..37ccb89 100644
--- a/ast-generator/src/build_fn_gen.rs
+++ b/ast-generator/src/build_fn_gen.rs
@@ -1,5 +1,6 @@
 use crate::spec::{
-    BuildBooleanOn, ChildSpec, SingleChildToBuild, StructBuildSpec, VecChildToBuild,
+    BuildBooleanOn, ChildSpec, SingleBooleanChildToBuild, SingleChildToBuild,
+    SingleTypeChildToBuild, StructBuildSpec, VecChild, VecChildToBuild,
 };
 use convert_case::{Case, Casing};
 use proc_macro2::TokenStream;
@@ -9,33 +10,45 @@ pub fn make_build_fn_name(s: &str) -> String {
     format!("build_{}", s.to_case(Case::Snake))
 }
 
+fn make_vec_child_holder(vec_child: &VecChild) -> TokenStream {
+    let (child_ident, child_type_ident) = match vec_child.build() {
+        VecChildToBuild::Type(vec_type_child) => (
+            format_ident!("{}", vec_type_child.var_name()),
+            format_ident!("{}", vec_type_child.build()),
+        ),
+    };
+    quote! {
+        let mut #child_ident: Vec<Box<#child_type_ident>> = vec![]
+    }
+}
+
+fn make_single_type_child_holder(single_type_child: &SingleTypeChildToBuild) -> TokenStream {
+    let child_ident = format_ident!("{}", single_type_child.var_name());
+    let child_type_ident = format_ident!("{}", single_type_child.build());
+    quote! {
+        let mut #child_ident: Option<Box<#child_type_ident>> = None
+    }
+}
+
+fn make_single_boolean_child_holder(
+    single_boolean_child: &SingleBooleanChildToBuild,
+) -> TokenStream {
+    let child_ident = format_ident!("{}", single_boolean_child.var_name());
+    quote! {
+        let mut #child_ident: bool = false
+    }
+}
+
 fn make_child_holder(child_spec: &ChildSpec) -> Option<TokenStream> {
     match child_spec {
         ChildSpec::SkipChild(_) => None,
-        ChildSpec::VecChild(vec_child) => {
-            let (child_ident, child_type_ident) = match vec_child.build() {
-                VecChildToBuild::Type(vec_type_child) => (
-                    format_ident!("{}", vec_type_child.var_name()),
-                    format_ident!("{}", vec_type_child.build()),
-                ),
-            };
-            Some(quote! {
-                let mut #child_ident: Vec<Box<#child_type_ident>> = vec![]
-            })
-        }
+        ChildSpec::VecChild(vec_child) => Some(make_vec_child_holder(vec_child)),
         ChildSpec::SingleChild(single_child) => match single_child.build() {
             SingleChildToBuild::Type(single_type_child) => {
-                let child_ident = format_ident!("{}", single_type_child.var_name());
-                let child_type_ident = format_ident!("{}", single_type_child.build());
-                Some(quote! {
-                    let mut #child_ident: Option<Box<#child_type_ident>> = None;
-                })
+                Some(make_single_type_child_holder(single_type_child))
             }
             SingleChildToBuild::Boolean(boolean_child) => {
-                let child_ident = format_ident!("{}", boolean_child.var_name());
-                Some(quote! {
-                    let #child_ident: bool = false
-                })
+                Some(make_single_boolean_child_holder(boolean_child))
             }
         },
     }
@@ -95,32 +108,32 @@ fn make_child_arg(child_spec: &ChildSpec) -> Option<TokenStream> {
         ChildSpec::SkipChild(_) => None,
         ChildSpec::VecChild(vec_child) => {
             let child_ident = match vec_child.build() {
-                VecChildToBuild::Type(vec_type_child) => format_ident!("{}", vec_type_child.var_name())
+                VecChildToBuild::Type(vec_type_child) => {
+                    format_ident!("{}", vec_type_child.var_name())
+                }
             };
             Some(quote! { #child_ident })
-        },
-        ChildSpec::SingleChild(single_child) => {
-            match single_child.build() {
-                SingleChildToBuild::Type(single_type_child) => {
-                    let child_ident = format_ident!("{}", single_type_child.var_name());
-                    if single_type_child.optional() {
-                        Some(quote! { #child_ident })
-                    } else if let Some(or_else) = single_type_child.or_else()  {
-                        let child_type_ident = format_ident!("{}", single_type_child.build());
-                        let or_else_ident = format_ident!("{}", or_else);
-                        Some(quote! {
-                            #child_ident.unwrap_or_else(|| Box::new(#child_type_ident::#or_else_ident()))
-                        })
-                    } else {
-                        Some(quote! { #child_ident.unwrap() })                        
-                    }
-                },
-                SingleChildToBuild::Boolean(single_boolean_child) => {
-                    let child_ident = format_ident!("{}", single_boolean_child.var_name());
+        }
+        ChildSpec::SingleChild(single_child) => match single_child.build() {
+            SingleChildToBuild::Type(single_type_child) => {
+                let child_ident = format_ident!("{}", single_type_child.var_name());
+                if single_type_child.optional() {
                     Some(quote! { #child_ident })
+                } else if let Some(or_else) = single_type_child.or_else() {
+                    let child_type_ident = format_ident!("{}", single_type_child.build());
+                    let or_else_ident = format_ident!("{}", or_else);
+                    Some(quote! {
+                        #child_ident.unwrap_or_else(|| Box::new(#child_type_ident::#or_else_ident()))
+                    })
+                } else {
+                    Some(quote! { #child_ident.unwrap() })
                 }
             }
-        }
+            SingleChildToBuild::Boolean(single_boolean_child) => {
+                let child_ident = format_ident!("{}", single_boolean_child.var_name());
+                Some(quote! { #child_ident })
+            }
+        },
     }
 }
 
@@ -180,3 +193,54 @@ pub fn make_struct_build_fn(build_spec: &StructBuildSpec) -> TokenStream {
         }
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::spec::VecTypeChildToBuild;
+
+    #[test]
+    fn vec_child_holder() {
+        let vec_child = VecChild::new(
+            "test_child",
+            "Test",
+            VecChildToBuild::Type(VecTypeChildToBuild::new(
+                "TestType",
+                "test_child",
+                "build_test_child",
+            )),
+        );
+        assert_eq!(
+            make_vec_child_holder(&vec_child).to_string(),
+            quote! {
+                let mut test_child: Vec<Box<TestType>> = vec![]
+            }
+            .to_string()
+        );
+    }
+
+    #[test]
+    fn single_type_child_holder() {
+        let single_type_child = SingleTypeChildToBuild::from_build_or_rule("TestType", None, false);
+        assert_eq!(
+            make_single_type_child_holder(&single_type_child).to_string(),
+            quote! {
+                let mut test_type: Option<Box<TestType>> = None
+            }
+            .to_string()
+        );
+    }
+
+    #[test]
+    fn single_boolean_child_holder() {
+        let single_boolean_child =
+            SingleBooleanChildToBuild::new("test_child", BuildBooleanOn::RulePresent);
+        assert_eq!(
+            make_single_boolean_child_holder(&single_boolean_child).to_string(),
+            quote! {
+                let mut test_child: bool = false
+            }
+            .to_string()
+        );
+    }
+}