diff --git a/erlang-term-format/src/lib.rs b/erlang-term-format/src/lib.rs
index 5ad67e1a6..7fff0f9bf 100644
--- a/erlang-term-format/src/lib.rs
+++ b/erlang-term-format/src/lib.rs
@@ -1,6 +1,9 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-FileCopyrightText: 2026 The Gleam contributors
 
+#[cfg(test)]
+mod tests;
+
 use num_bigint::{BigInt, Sign};
 use num_traits::ToPrimitive;
 
@@ -10,13 +13,20 @@ extern crate pretty_assertions;
 
 #[must_use]
 #[derive(Debug)]
-pub struct List {
+pub struct ListEnder {
+    /// This is the index in the term builder buffer to where the number of
+    /// elements in the list is written. When we start a list the number is
+    /// zeroed as we may not know the number of elements yet, and it is
+    /// written when finishing the list using this index.
     size_index: usize,
+
+    /// This field is used by the debug mode `Drop` implementation, to ensure
+    /// that lists are correctly closed after being consumed.
     #[cfg(debug_assertions)]
     used: bool,
 }
 
-impl List {
+impl ListEnder {
     pub fn new(size_index: usize) -> Self {
         Self {
             size_index,
@@ -27,45 +37,49 @@ impl List {
     }
 }
 
-#[cfg(debug_assertions)]
-impl List {
+impl ListEnder {
+    #[cfg(debug_assertions)]
     pub fn consume(mut self) {
         self.used = true;
     }
-}
 
-#[cfg(not(debug_assertions))]
-impl List {
+    #[cfg(not(debug_assertions))]
     pub fn consume(self) {}
 }
 
 /// When testing we want to make sure that all lists are always correctly closed
-/// after being consumed. In production builds all of these operations become
-/// no-ops.
+/// after being consumed. In production builds this is not implemented, so there
+/// is no runtime cost.
 #[cfg(debug_assertions)]
-impl Drop for List {
+impl Drop for ListEnder {
     fn drop(&mut self) {
         assert!(self.used, "list not closed");
     }
 }
 
+/// The first byte of ETF data is this version number.
+///
+const ERLANG_TERM_FORMAT_VERSION_NUMBER: u8 = 131;
+
 /// A data structure used to encode values into the Erlang Term Format:
 /// https://www.erlang.org/doc/apps/erts/erl_ext_dist.html.
 ///
 #[derive(Debug)]
-pub struct Builder {
+pub struct TermBuilder {
     bytes: Vec<u8>,
 }
 
-impl Default for Builder {
+impl Default for TermBuilder {
     fn default() -> Self {
         Self::new()
     }
 }
 
-impl Builder {
+impl TermBuilder {
     pub fn new() -> Self {
-        Self { bytes: vec![131] }
+        Self {
+            bytes: vec![ERLANG_TERM_FORMAT_VERSION_NUMBER],
+        }
     }
 
     /// Get the binary representation of the data structure built so far.
@@ -103,19 +117,25 @@ impl Builder {
     /// ```
     ///
     /// https://www.erlang.org/doc/apps/erts/erl_ext_dist.html#list_ext
-    pub fn start_list(&mut self) -> List {
+    pub fn start_list(&mut self) -> ListEnder {
         self.push(108);
         let size_index = self.bytes.len();
+
+        // These 4 bytes store the number of elements (not including the tail).
+        // They are set to zero here, and the `end_list` function overwrites them
+        // with the actual length, as that number may not be known in advance.
         self.push(0);
         self.push(0);
         self.push(0);
         self.push(0);
-        List::new(size_index)
+
+        ListEnder::new(size_index)
     }
 
-    pub fn end_list(&mut self, list: List, items: u32) {
+    pub fn end_list(&mut self, list: ListEnder, number_of_element: u32) {
         self.empty_list();
-        self.bytes[list.size_index..list.size_index + 4].copy_from_slice(&items.to_be_bytes());
+        self.bytes[list.size_index..list.size_index + 4]
+            .copy_from_slice(&number_of_element.to_be_bytes());
         list.consume();
     }
 
@@ -233,388 +253,3 @@ impl Builder {
         self.extend(name.bytes());
     }
 }
-
-#[cfg(test)]
-/// We want to test all of these functions against the actual values produced by
-/// Erlang when turning some data into a binary.
-///
-/// All the bytes you see in the assertions here were produced using the
-/// following bit of Erlang:
-///
-/// ```erl
-/// Binary = term_to_binary(SomeErlangData),
-/// io:format("~w~n", [Binary]).
-/// ```
-///
-/// This will turn any data structure into its binary representation and print
-/// its bytes we can then copy paste in these tests.
-///
-/// For example: if I were to test that a list of two atoms is correctly turned
-/// into its binary representation I would write the following:
-///
-/// ```erl
-/// Binary = term_to_binary([nil, ok]),
-/// io:format("~w~n", [Binary]).
-/// ```
-///
-/// And write a test like this:
-///
-/// ```ignore
-/// let mut etf = Builder::new();
-/// let list = etf.start_list();
-/// etf.atom("nil");
-/// etf.atom("ok");
-/// etf.end_list(list, 2);
-///
-/// assert_eq!(
-///     etf.into_vec(),
-///     [... the bytes I got from the Erlang code ...]
-/// )
-/// ```
-///
-mod tests {
-    use std::{ops::Neg, str::FromStr};
-
-    use num_bigint::BigInt;
-
-    use crate::Builder;
-
-    #[test]
-    fn small_atom() {
-        let mut etf = Builder::new();
-        etf.atom("atom");
-        assert_eq!(etf.into_vec(), [131, 119, 4, 97, 116, 111, 109])
-    }
-
-    #[test]
-    fn small_atom_utf8() {
-        let mut etf = Builder::new();
-        etf.atom("ksiąskę");
-        assert_eq!(
-            etf.into_vec(),
-            [131, 119, 9, 107, 115, 105, 196, 133, 115, 107, 196, 153]
-        )
-    }
-
-    #[test]
-    fn atom() {
-        let mut etf = Builder::new();
-        etf.atom(&"ą".repeat(128));
-        assert_eq!(
-            etf.into_vec(),
-            [
-                131, 118, 1, 0, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
-                133, 196, 133
-            ]
-        )
-    }
-
-    #[test]
-    fn small_integer() {
-        let mut etf = Builder::new();
-        etf.small_integer(1);
-        assert_eq!(etf.into_vec(), [131, 97, 1]);
-    }
-
-    #[test]
-    fn integer() {
-        let mut etf = Builder::new();
-        etf.integer(-2);
-        assert_eq!(etf.into_vec(), [131, 98, 255, 255, 255, 254]);
-    }
-
-    #[test]
-    fn integer_2() {
-        let mut etf = Builder::new();
-        etf.integer(1048576);
-        assert_eq!(etf.into_vec(), [131, 98, 0, 16, 0, 0]);
-    }
-
-    #[test]
-    fn float() {
-        let mut etf = Builder::new();
-        etf.new_float(1.2);
-        assert_eq!(etf.into_vec(), [131, 70, 63, 243, 51, 51, 51, 51, 51, 51])
-    }
-
-    #[test]
-    fn small_big() {
-        let mut etf = Builder::new();
-
-        etf.small_big(BigInt::from(123123123123123123 as i64));
-        assert_eq!(
-            etf.into_vec(),
-            [131, 110, 8, 0, 179, 243, 99, 1, 212, 107, 181, 1]
-        );
-    }
-
-    #[test]
-    fn negative_small_big() {
-        let mut etf = Builder::new();
-        etf.small_big(BigInt::from(-123123123123123123 as i64));
-        assert_eq!(
-            etf.into_vec(),
-            [131, 110, 8, 1, 179, 243, 99, 1, 212, 107, 181, 1]
-        );
-    }
-
-    #[test]
-    fn empty_list() {
-        let mut etf = Builder::new();
-        etf.empty_list();
-        assert_eq!(etf.into_vec(), [131, 106]);
-    }
-
-    #[test]
-    fn proper_list_with_a_single_item() {
-        let mut etf = Builder::new();
-        let list = etf.start_list();
-        etf.small_integer(1);
-        etf.end_list(list, 1);
-        assert_eq!(etf.into_vec(), [131, 108, 0, 0, 0, 1, 97, 1, 106])
-    }
-
-    #[test]
-    fn proper_list() {
-        let mut etf = Builder::new();
-        let list = etf.start_list();
-        etf.small_integer(1);
-        etf.small_tuple(0);
-        etf.small_integer(2);
-        etf.end_list(list, 3);
-        assert_eq!(
-            etf.into_vec(),
-            [131, 108, 0, 0, 0, 3, 97, 1, 104, 0, 97, 2, 106]
-        )
-    }
-
-    #[test]
-    fn empty_binary() {
-        let mut etf = Builder::new();
-        etf.binary(0, vec![]);
-        assert_eq!(etf.into_vec(), [131, 109, 0, 0, 0, 0])
-    }
-    #[test]
-    fn binary() {
-        let mut etf = Builder::new();
-        etf.binary(3, vec![1, 2, 3]);
-        assert_eq!(etf.into_vec(), [131, 109, 0, 0, 0, 3, 1, 2, 3])
-    }
-
-    #[test]
-    fn small_empty_tuple() {
-        let mut etf = Builder::new();
-        etf.small_tuple(0);
-        assert_eq!(etf.into_vec(), [131, 104, 0])
-    }
-
-    #[test]
-    fn small_single_item_tuple() {
-        let mut etf = Builder::new();
-        etf.small_tuple(1);
-        etf.small_integer(1);
-        assert_eq!(etf.into_vec(), [131, 104, 1, 97, 1])
-    }
-
-    #[test]
-    fn small_tuple() {
-        let mut etf = Builder::new();
-        etf.small_tuple(3);
-        etf.new_float(1.1);
-        etf.integer(-1);
-        etf.small_integer(11);
-
-        assert_eq!(
-            etf.into_vec(),
-            [
-                131, 104, 3, 70, 63, 241, 153, 153, 153, 153, 153, 154, 98, 255, 255, 255, 255, 97,
-                11
-            ]
-        )
-    }
-
-    #[test]
-    fn small_nested_tuple() {
-        let mut etf = Builder::new();
-        etf.small_tuple(2);
-
-        etf.small_tuple(2);
-        etf.small_integer(1);
-        etf.small_integer(11);
-
-        etf.small_tuple(1);
-        etf.new_float(1.1);
-
-        assert_eq!(
-            etf.into_vec(),
-            [
-                131, 104, 2, 104, 2, 97, 1, 97, 11, 104, 1, 70, 63, 241, 153, 153, 153, 153, 153,
-                154
-            ]
-        )
-    }
-
-    #[test]
-    fn large_tuple() {
-        let mut etf = Builder::new();
-        etf.large_tuple(500);
-        for _ in 1..=500 {
-            etf.small_integer(1);
-        }
-
-        assert_eq!(
-            etf.into_vec(),
-            [
-                131, 105, 0, 0, 1, 244, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
-                1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1
-            ]
-        )
-    }
-
-    #[test]
-    fn large_big() {
-        let mut etf = Builder::new();
-        etf.large_big(BigInt::from_str(&"1".repeat(1500)).unwrap());
-        assert_eq!(
-            etf.into_vec(),
-            [
-                131, 111, 0, 0, 2, 111, 0, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 1, 169, 242, 20, 147,
-                190, 32, 128, 194, 36, 247, 163, 33, 20, 52, 44, 99, 21, 192, 66, 245, 84, 128, 97,
-                156, 59, 26, 49, 215, 19, 60, 165, 65, 99, 28, 91, 91, 132, 187, 191, 48, 27, 217,
-                244, 127, 22, 229, 191, 10, 184, 4, 38, 105, 182, 90, 90, 141, 23, 179, 148, 140,
-                187, 169, 145, 218, 132, 199, 136, 139, 1, 228, 120, 218, 220, 103, 20, 164, 155,
-                60, 1, 158, 242, 71, 1, 60, 69, 6, 13, 244, 52, 42, 222, 129, 25, 127, 251, 133,
-                199, 37, 61, 61, 94, 35, 52, 38, 9, 114, 0, 173, 92, 189, 59, 8, 14, 253, 129, 64,
-                238, 18, 222, 214, 221, 45, 236, 250, 62, 255, 237, 241, 149, 145, 143, 93, 41, 2,
-                156, 28, 29, 102, 103, 8, 227, 146, 128, 117, 183, 231, 113, 20, 148, 190, 253, 95,
-                114, 208, 224, 186, 125, 28, 74, 117, 131, 197, 189, 238, 208, 96, 253, 134, 27,
-                108, 58, 63, 97, 183, 248, 49, 174, 205, 42, 129, 196, 241, 71, 237, 83, 136, 127,
-                61, 225, 107, 199, 146, 30, 212, 53, 215, 141, 147, 198, 3, 37, 170, 175, 29, 43,
-                85, 98, 73, 198, 113, 9, 121, 149, 228, 107, 200, 16, 159, 117, 150, 91, 90, 121,
-                11, 5, 27, 25, 110, 69, 194, 57, 21, 91, 173, 149, 40, 5, 126, 101, 113, 247, 14,
-                130, 154, 249, 36, 143, 183, 129, 4, 174, 108, 164, 122, 95, 105, 77, 243, 58, 158,
-                223, 166, 79, 103, 131, 161, 110, 57, 79, 214, 142, 141, 39, 101, 6, 176, 22, 182,
-                89, 247, 229, 80, 244, 24, 62, 101, 128, 174, 253, 86, 233, 138, 130, 115, 157, 80,
-                21, 83, 187, 222, 43, 19, 105, 97, 230, 7, 167, 25, 6, 69, 207, 149, 32, 199, 44,
-                85, 27, 223, 133, 46, 234, 3, 59, 113, 228, 246, 29, 157, 4, 83, 207, 234, 85, 122,
-                148, 64, 125, 49, 48, 123, 226, 213, 154, 212, 102, 6, 154, 91, 67, 242, 232, 99,
-                154, 238, 73, 72, 122, 170, 27, 110, 83, 110, 146, 159, 87, 87, 163, 151, 196, 47,
-                134, 198, 170, 197, 189, 176, 82, 247, 130, 95, 159, 217, 228, 52, 214, 63, 247,
-                169, 152, 216, 23, 182, 142, 26, 218, 248, 47, 161, 238, 180, 122, 54, 239, 38, 95,
-                65, 114, 128, 93, 233, 71, 177, 101, 2, 236, 244, 88, 249, 104, 210, 4, 249, 5,
-                172, 107, 216, 222, 165, 242, 106, 222, 22, 158, 50, 13
-            ]
-        );
-    }
-
-    #[test]
-    fn negative_large_big() {
-        let mut etf = Builder::new();
-        etf.large_big(BigInt::from_str(&"1".repeat(1500)).unwrap().neg());
-        assert_eq!(
-            etf.into_vec(),
-            [
-                131, 111, 0, 0, 2, 111, 1, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28,
-                199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 1, 169, 242, 20, 147,
-                190, 32, 128, 194, 36, 247, 163, 33, 20, 52, 44, 99, 21, 192, 66, 245, 84, 128, 97,
-                156, 59, 26, 49, 215, 19, 60, 165, 65, 99, 28, 91, 91, 132, 187, 191, 48, 27, 217,
-                244, 127, 22, 229, 191, 10, 184, 4, 38, 105, 182, 90, 90, 141, 23, 179, 148, 140,
-                187, 169, 145, 218, 132, 199, 136, 139, 1, 228, 120, 218, 220, 103, 20, 164, 155,
-                60, 1, 158, 242, 71, 1, 60, 69, 6, 13, 244, 52, 42, 222, 129, 25, 127, 251, 133,
-                199, 37, 61, 61, 94, 35, 52, 38, 9, 114, 0, 173, 92, 189, 59, 8, 14, 253, 129, 64,
-                238, 18, 222, 214, 221, 45, 236, 250, 62, 255, 237, 241, 149, 145, 143, 93, 41, 2,
-                156, 28, 29, 102, 103, 8, 227, 146, 128, 117, 183, 231, 113, 20, 148, 190, 253, 95,
-                114, 208, 224, 186, 125, 28, 74, 117, 131, 197, 189, 238, 208, 96, 253, 134, 27,
-                108, 58, 63, 97, 183, 248, 49, 174, 205, 42, 129, 196, 241, 71, 237, 83, 136, 127,
-                61, 225, 107, 199, 146, 30, 212, 53, 215, 141, 147, 198, 3, 37, 170, 175, 29, 43,
-                85, 98, 73, 198, 113, 9, 121, 149, 228, 107, 200, 16, 159, 117, 150, 91, 90, 121,
-                11, 5, 27, 25, 110, 69, 194, 57, 21, 91, 173, 149, 40, 5, 126, 101, 113, 247, 14,
-                130, 154, 249, 36, 143, 183, 129, 4, 174, 108, 164, 122, 95, 105, 77, 243, 58, 158,
-                223, 166, 79, 103, 131, 161, 110, 57, 79, 214, 142, 141, 39, 101, 6, 176, 22, 182,
-                89, 247, 229, 80, 244, 24, 62, 101, 128, 174, 253, 86, 233, 138, 130, 115, 157, 80,
-                21, 83, 187, 222, 43, 19, 105, 97, 230, 7, 167, 25, 6, 69, 207, 149, 32, 199, 44,
-                85, 27, 223, 133, 46, 234, 3, 59, 113, 228, 246, 29, 157, 4, 83, 207, 234, 85, 122,
-                148, 64, 125, 49, 48, 123, 226, 213, 154, 212, 102, 6, 154, 91, 67, 242, 232, 99,
-                154, 238, 73, 72, 122, 170, 27, 110, 83, 110, 146, 159, 87, 87, 163, 151, 196, 47,
-                134, 198, 170, 197, 189, 176, 82, 247, 130, 95, 159, 217, 228, 52, 214, 63, 247,
-                169, 152, 216, 23, 182, 142, 26, 218, 248, 47, 161, 238, 180, 122, 54, 239, 38, 95,
-                65, 114, 128, 93, 233, 71, 177, 101, 2, 236, 244, 88, 249, 104, 210, 4, 249, 5,
-                172, 107, 216, 222, 165, 242, 106, 222, 22, 158, 50, 13
-            ]
-        );
-    }
-}
diff --git a/erlang-term-format/src/tests.rs b/erlang-term-format/src/tests.rs
new file mode 100644
index 000000000..4e914f086
--- /dev/null
+++ b/erlang-term-format/src/tests.rs
@@ -0,0 +1,378 @@
+// SPDX-License-Identifier: Apache-2.0
+// SPDX-FileCopyrightText: 2026 The Gleam contributors
+
+//// We want to test all of these functions against the actual values produced by
+//// Erlang when turning some data into a binary.
+////
+//// All the bytes you see in the assertions here were produced using the
+//// following bit of Erlang:
+////
+//// ```erl
+//// Binary = term_to_binary(SomeErlangData),
+//// io:format("~w~n", [Binary]).
+//// ```
+////
+//// This will turn any data structure into its binary representation and print
+//// its bytes we can then copy paste in these tests.
+////
+//// For example: if I were to test that a list of two atoms is correctly turned
+//// into its binary representation I would write the following:
+////
+//// ```erl
+//// Binary = term_to_binary([nil, ok]),
+//// io:format("~w~n", [Binary]).
+//// ```
+////
+//// And write a test like this:
+////
+//// ```ignore
+//// let mut etf = Builder::new();
+//// let list = etf.start_list();
+//// etf.atom("nil");
+//// etf.atom("ok");
+//// etf.end_list(list, 2);
+////
+//// assert_eq!(
+////     etf.into_vec(),
+////     [... the bytes I got from the Erlang code ...]
+//// )
+//// ```
+////
+use std::{ops::Neg, str::FromStr};
+
+use num_bigint::BigInt;
+
+use crate::TermBuilder;
+
+#[test]
+fn small_atom() {
+    let mut etf = TermBuilder::new();
+    etf.atom("atom");
+    assert_eq!(etf.into_vec(), [131, 119, 4, 97, 116, 111, 109])
+}
+
+#[test]
+fn small_atom_utf8() {
+    let mut etf = TermBuilder::new();
+    etf.atom("ksiąskę");
+    assert_eq!(
+        etf.into_vec(),
+        [131, 119, 9, 107, 115, 105, 196, 133, 115, 107, 196, 153]
+    )
+}
+
+#[test]
+fn atom() {
+    let mut etf = TermBuilder::new();
+    etf.atom(&"ą".repeat(128));
+    assert_eq!(
+        etf.into_vec(),
+        [
+            131, 118, 1, 0, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196,
+            133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133, 196, 133,
+            196, 133, 196, 133
+        ]
+    )
+}
+
+#[test]
+fn small_integer() {
+    let mut etf = TermBuilder::new();
+    etf.small_integer(1);
+    assert_eq!(etf.into_vec(), [131, 97, 1]);
+}
+
+#[test]
+fn integer() {
+    let mut etf = TermBuilder::new();
+    etf.integer(-2);
+    assert_eq!(etf.into_vec(), [131, 98, 255, 255, 255, 254]);
+}
+
+#[test]
+fn integer_2() {
+    let mut etf = TermBuilder::new();
+    etf.integer(1048576);
+    assert_eq!(etf.into_vec(), [131, 98, 0, 16, 0, 0]);
+}
+
+#[test]
+fn float() {
+    let mut etf = TermBuilder::new();
+    etf.new_float(1.2);
+    assert_eq!(etf.into_vec(), [131, 70, 63, 243, 51, 51, 51, 51, 51, 51])
+}
+
+#[test]
+fn small_big() {
+    let mut etf = TermBuilder::new();
+
+    etf.small_big(BigInt::from(123123123123123123 as i64));
+    assert_eq!(
+        etf.into_vec(),
+        [131, 110, 8, 0, 179, 243, 99, 1, 212, 107, 181, 1]
+    );
+}
+
+#[test]
+fn negative_small_big() {
+    let mut etf = TermBuilder::new();
+    etf.small_big(BigInt::from(-123123123123123123 as i64));
+    assert_eq!(
+        etf.into_vec(),
+        [131, 110, 8, 1, 179, 243, 99, 1, 212, 107, 181, 1]
+    );
+}
+
+#[test]
+fn empty_list() {
+    let mut etf = TermBuilder::new();
+    etf.empty_list();
+    assert_eq!(etf.into_vec(), [131, 106]);
+}
+
+#[test]
+fn proper_list_with_a_single_item() {
+    let mut etf = TermBuilder::new();
+    let list = etf.start_list();
+    etf.small_integer(1);
+    etf.end_list(list, 1);
+    assert_eq!(etf.into_vec(), [131, 108, 0, 0, 0, 1, 97, 1, 106])
+}
+
+#[test]
+fn proper_list() {
+    let mut etf = TermBuilder::new();
+    let list = etf.start_list();
+    etf.small_integer(1);
+    etf.small_tuple(0);
+    etf.small_integer(2);
+    etf.end_list(list, 3);
+    assert_eq!(
+        etf.into_vec(),
+        [131, 108, 0, 0, 0, 3, 97, 1, 104, 0, 97, 2, 106]
+    )
+}
+
+#[test]
+fn empty_binary() {
+    let mut etf = TermBuilder::new();
+    etf.binary(0, vec![]);
+    assert_eq!(etf.into_vec(), [131, 109, 0, 0, 0, 0])
+}
+#[test]
+fn binary() {
+    let mut etf = TermBuilder::new();
+    etf.binary(3, vec![1, 2, 3]);
+    assert_eq!(etf.into_vec(), [131, 109, 0, 0, 0, 3, 1, 2, 3])
+}
+
+#[test]
+fn small_empty_tuple() {
+    let mut etf = TermBuilder::new();
+    etf.small_tuple(0);
+    assert_eq!(etf.into_vec(), [131, 104, 0])
+}
+
+#[test]
+fn small_single_item_tuple() {
+    let mut etf = TermBuilder::new();
+    etf.small_tuple(1);
+    etf.small_integer(1);
+    assert_eq!(etf.into_vec(), [131, 104, 1, 97, 1])
+}
+
+#[test]
+fn small_tuple() {
+    let mut etf = TermBuilder::new();
+    etf.small_tuple(3);
+    etf.new_float(1.1);
+    etf.integer(-1);
+    etf.small_integer(11);
+
+    assert_eq!(
+        etf.into_vec(),
+        [
+            131, 104, 3, 70, 63, 241, 153, 153, 153, 153, 153, 154, 98, 255, 255, 255, 255, 97, 11
+        ]
+    )
+}
+
+#[test]
+fn small_nested_tuple() {
+    let mut etf = TermBuilder::new();
+    etf.small_tuple(2);
+
+    etf.small_tuple(2);
+    etf.small_integer(1);
+    etf.small_integer(11);
+
+    etf.small_tuple(1);
+    etf.new_float(1.1);
+
+    assert_eq!(
+        etf.into_vec(),
+        [
+            131, 104, 2, 104, 2, 97, 1, 97, 11, 104, 1, 70, 63, 241, 153, 153, 153, 153, 153, 154
+        ]
+    )
+}
+
+#[test]
+fn large_tuple() {
+    let mut etf = TermBuilder::new();
+    etf.large_tuple(500);
+    for _ in 1..=500 {
+        etf.small_integer(1);
+    }
+
+    assert_eq!(
+        etf.into_vec(),
+        [
+            131, 105, 0, 0, 1, 244, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1,
+            97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97, 1, 97,
+            1, 97, 1, 97, 1, 97, 1
+        ]
+    )
+}
+
+#[test]
+fn large_big() {
+    let mut etf = TermBuilder::new();
+    etf.large_big(BigInt::from_str(&"1".repeat(1500)).unwrap());
+    assert_eq!(
+        etf.into_vec(),
+        [
+            131, 111, 0, 0, 2, 111, 0, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 1, 169, 242, 20, 147, 190, 32,
+            128, 194, 36, 247, 163, 33, 20, 52, 44, 99, 21, 192, 66, 245, 84, 128, 97, 156, 59, 26,
+            49, 215, 19, 60, 165, 65, 99, 28, 91, 91, 132, 187, 191, 48, 27, 217, 244, 127, 22,
+            229, 191, 10, 184, 4, 38, 105, 182, 90, 90, 141, 23, 179, 148, 140, 187, 169, 145, 218,
+            132, 199, 136, 139, 1, 228, 120, 218, 220, 103, 20, 164, 155, 60, 1, 158, 242, 71, 1,
+            60, 69, 6, 13, 244, 52, 42, 222, 129, 25, 127, 251, 133, 199, 37, 61, 61, 94, 35, 52,
+            38, 9, 114, 0, 173, 92, 189, 59, 8, 14, 253, 129, 64, 238, 18, 222, 214, 221, 45, 236,
+            250, 62, 255, 237, 241, 149, 145, 143, 93, 41, 2, 156, 28, 29, 102, 103, 8, 227, 146,
+            128, 117, 183, 231, 113, 20, 148, 190, 253, 95, 114, 208, 224, 186, 125, 28, 74, 117,
+            131, 197, 189, 238, 208, 96, 253, 134, 27, 108, 58, 63, 97, 183, 248, 49, 174, 205, 42,
+            129, 196, 241, 71, 237, 83, 136, 127, 61, 225, 107, 199, 146, 30, 212, 53, 215, 141,
+            147, 198, 3, 37, 170, 175, 29, 43, 85, 98, 73, 198, 113, 9, 121, 149, 228, 107, 200,
+            16, 159, 117, 150, 91, 90, 121, 11, 5, 27, 25, 110, 69, 194, 57, 21, 91, 173, 149, 40,
+            5, 126, 101, 113, 247, 14, 130, 154, 249, 36, 143, 183, 129, 4, 174, 108, 164, 122, 95,
+            105, 77, 243, 58, 158, 223, 166, 79, 103, 131, 161, 110, 57, 79, 214, 142, 141, 39,
+            101, 6, 176, 22, 182, 89, 247, 229, 80, 244, 24, 62, 101, 128, 174, 253, 86, 233, 138,
+            130, 115, 157, 80, 21, 83, 187, 222, 43, 19, 105, 97, 230, 7, 167, 25, 6, 69, 207, 149,
+            32, 199, 44, 85, 27, 223, 133, 46, 234, 3, 59, 113, 228, 246, 29, 157, 4, 83, 207, 234,
+            85, 122, 148, 64, 125, 49, 48, 123, 226, 213, 154, 212, 102, 6, 154, 91, 67, 242, 232,
+            99, 154, 238, 73, 72, 122, 170, 27, 110, 83, 110, 146, 159, 87, 87, 163, 151, 196, 47,
+            134, 198, 170, 197, 189, 176, 82, 247, 130, 95, 159, 217, 228, 52, 214, 63, 247, 169,
+            152, 216, 23, 182, 142, 26, 218, 248, 47, 161, 238, 180, 122, 54, 239, 38, 95, 65, 114,
+            128, 93, 233, 71, 177, 101, 2, 236, 244, 88, 249, 104, 210, 4, 249, 5, 172, 107, 216,
+            222, 165, 242, 106, 222, 22, 158, 50, 13
+        ]
+    );
+}
+
+#[test]
+fn negative_large_big() {
+    let mut etf = TermBuilder::new();
+    etf.large_big(BigInt::from_str(&"1".repeat(1500)).unwrap().neg());
+    assert_eq!(
+        etf.into_vec(),
+        [
+            131, 111, 0, 0, 2, 111, 1, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199,
+            113, 28, 199, 113, 28, 199, 113, 28, 199, 113, 28, 199, 1, 169, 242, 20, 147, 190, 32,
+            128, 194, 36, 247, 163, 33, 20, 52, 44, 99, 21, 192, 66, 245, 84, 128, 97, 156, 59, 26,
+            49, 215, 19, 60, 165, 65, 99, 28, 91, 91, 132, 187, 191, 48, 27, 217, 244, 127, 22,
+            229, 191, 10, 184, 4, 38, 105, 182, 90, 90, 141, 23, 179, 148, 140, 187, 169, 145, 218,
+            132, 199, 136, 139, 1, 228, 120, 218, 220, 103, 20, 164, 155, 60, 1, 158, 242, 71, 1,
+            60, 69, 6, 13, 244, 52, 42, 222, 129, 25, 127, 251, 133, 199, 37, 61, 61, 94, 35, 52,
+            38, 9, 114, 0, 173, 92, 189, 59, 8, 14, 253, 129, 64, 238, 18, 222, 214, 221, 45, 236,
+            250, 62, 255, 237, 241, 149, 145, 143, 93, 41, 2, 156, 28, 29, 102, 103, 8, 227, 146,
+            128, 117, 183, 231, 113, 20, 148, 190, 253, 95, 114, 208, 224, 186, 125, 28, 74, 117,
+            131, 197, 189, 238, 208, 96, 253, 134, 27, 108, 58, 63, 97, 183, 248, 49, 174, 205, 42,
+            129, 196, 241, 71, 237, 83, 136, 127, 61, 225, 107, 199, 146, 30, 212, 53, 215, 141,
+            147, 198, 3, 37, 170, 175, 29, 43, 85, 98, 73, 198, 113, 9, 121, 149, 228, 107, 200,
+            16, 159, 117, 150, 91, 90, 121, 11, 5, 27, 25, 110, 69, 194, 57, 21, 91, 173, 149, 40,
+            5, 126, 101, 113, 247, 14, 130, 154, 249, 36, 143, 183, 129, 4, 174, 108, 164, 122, 95,
+            105, 77, 243, 58, 158, 223, 166, 79, 103, 131, 161, 110, 57, 79, 214, 142, 141, 39,
+            101, 6, 176, 22, 182, 89, 247, 229, 80, 244, 24, 62, 101, 128, 174, 253, 86, 233, 138,
+            130, 115, 157, 80, 21, 83, 187, 222, 43, 19, 105, 97, 230, 7, 167, 25, 6, 69, 207, 149,
+            32, 199, 44, 85, 27, 223, 133, 46, 234, 3, 59, 113, 228, 246, 29, 157, 4, 83, 207, 234,
+            85, 122, 148, 64, 125, 49, 48, 123, 226, 213, 154, 212, 102, 6, 154, 91, 67, 242, 232,
+            99, 154, 238, 73, 72, 122, 170, 27, 110, 83, 110, 146, 159, 87, 87, 163, 151, 196, 47,
+            134, 198, 170, 197, 189, 176, 82, 247, 130, 95, 159, 217, 228, 52, 214, 63, 247, 169,
+            152, 216, 23, 182, 142, 26, 218, 248, 47, 161, 238, 180, 122, 54, 239, 38, 95, 65, 114,
+            128, 93, 233, 71, 177, 101, 2, 236, 244, 88, 249, 104, 210, 4, 249, 5, 172, 107, 216,
+            222, 165, 242, 106, 222, 22, 158, 50, 13
+        ]
+    );
+}