diff --git a/compiler-cli/src/add.rs b/compiler-cli/src/add.rs
index 7c0390771..b97bf1eae 100644
--- a/compiler-cli/src/add.rs
+++ b/compiler-cli/src/add.rs
@@ -114,11 +114,12 @@ fn read_toml_edit(name: &Utf8Path) -> Result<toml_edit::DocumentMut, Error> {
 
 fn version_to_string(version: &Version) -> String {
     let mut text = String::new();
-    let _ = write!(
+    write!(
         text,
         "{}.{}.{}",
         version.major, version.minor, version.patch
-    );
+    )
+    .expect("write to a string");
 
     if !version.pre.is_empty() {
         text.push('-');
@@ -133,7 +134,8 @@ fn version_to_string(version: &Version) -> String {
         }
     }
     if let Some(build) = version.build.as_ref() {
-        let _ = write!(text, "+{build}");
+        text.push('+');
+        text.push_str(build);
     }
     text
 }
diff --git a/compiler-core/src/derivation_tree.rs b/compiler-core/src/derivation_tree.rs
index 7305317ae..75ebe3225 100644
--- a/compiler-core/src/derivation_tree.rs
+++ b/compiler-core/src/derivation_tree.rs
@@ -13,7 +13,6 @@ use petgraph::prelude::StableGraph;
 use pubgrub::External;
 use pubgrub::{DerivationTree, Derived, Ranges};
 use std::collections::HashMap;
-use std::fmt::Write as _;
 use std::hash::RandomState;
 use std::ops::Bound::{Excluded, Included, Unbounded};
 use std::sync::Arc;
@@ -172,11 +171,13 @@ impl DerivationTreePrinter {
                 .ranges_between(previous, next)
                 .expect("path edge is in the graph");
 
-            let _ = write!(
-                message,
-                "\n    - {previous_name} requires {next_name} {}",
-                pretty_range(next_range)
-            );
+            message.push_str("\n    - ");
+            message.push_str(previous_name);
+            message.push_str(" requires ");
+            message.push_str(next_name);
+            message.push(' ');
+            message.push_str(&pretty_range(next_range));
+
             previous = next;
         }
         message
diff --git a/compiler-core/src/docs/tests.rs b/compiler-core/src/docs/tests.rs
index b2d8440a7..06cd66f4b 100644
--- a/compiler-core/src/docs/tests.rs
+++ b/compiler-core/src/docs/tests.rs
@@ -3,7 +3,6 @@
 
 use std::{
     collections::{HashMap, HashSet},
-    fmt::Write as _,
     time::SystemTime,
 };
 
@@ -201,7 +200,11 @@ fn compile_documentation(
 
     output.push_str("---- SOURCE CODE\n");
     for (_package, name, src) in modules {
-        let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+        output.push_str("-- ");
+        output.push_str(name);
+        output.push_str(".gleam\n");
+        output.push_str(src);
+        output.push_str("\n\n");
     }
     output.push_str("-- ");
     output.push_str(module_name);
diff --git a/compiler-core/src/error.rs b/compiler-core/src/error.rs
index f8c2fb7bd..268abc0c4 100644
--- a/compiler-core/src/error.rs
+++ b/compiler-core/src/error.rs
@@ -7,7 +7,6 @@ use crate::bit_array::UnsupportedOption;
 use crate::build::{Origin, Outcome, Runtime, Target};
 use crate::dependency::{PackageFetcher, ResolutionError};
 use crate::diagnostic::{Diagnostic, ExtraLabel, Label, Location};
-use std::fmt::Write as _;
 
 use crate::derivation_tree::DerivationTreePrinter;
 use crate::parse::error::ParseErrorDetails;
@@ -3536,7 +3535,11 @@ but no type in scope with that name."
                         };
                         text.push_str(message);
                         for module_name in possible_modules {
-                            let _ = writeln!(text, "  - {module_name}.{name}");
+                            text.push_str("  - ");
+                            text.push_str(module_name);
+                            text.push('.');
+                            text.push_str(name);
+                            text.push('\n');
                         }
                     }
 
@@ -4649,11 +4652,9 @@ here takes {expected_string}.\n"
 the `use` callback function.\n",
                     );
                 } else {
-                    let _ = writeln!(
-                        text,
-                        "You supplied {supplied_arguments_string} \
-and the final one is the `use` callback function."
-                    );
+                    text.push_str("You supplied ");
+                    text.push_str(&supplied_arguments_string);
+                    text.push_str(" and the final one is the `use` callback function.\n");
                 }
             } else {
                 text.push_str(
diff --git a/compiler-core/src/javascript/tests.rs b/compiler-core/src/javascript/tests.rs
index f1d5214d6..72c7c8359 100644
--- a/compiler-core/src/javascript/tests.rs
+++ b/compiler-core/src/javascript/tests.rs
@@ -47,14 +47,21 @@ pub static CURRENT_PACKAGE: &str = "thepackage";
 #[macro_export]
 macro_rules! assert_js {
     ($(($name:literal, $module_src:literal)),+, $src:literal $(,)?) => {
-        use std::fmt::Write as _;
         let compiled =
             $crate::javascript::tests::compile_js($src, vec![$(($crate::javascript::tests::CURRENT_PACKAGE, $name, $module_src)),*]);
             let mut output = String::from("----- SOURCE CODE\n");
             for (name, src) in [$(($name, $module_src)),*] {
-                let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+                output.push_str("-- ");
+                output.push_str(name);
+                output.push_str(".gleam\n");
+                output.push_str(src);
+                output.push_str("\n\n");
             }
-            let _ = write!(output, "-- main.gleam\n{}\n\n----- COMPILED JAVASCRIPT\n{compiled}", $src);
+            output.push_str("-- main.gleam\n");
+            output.push_str($src);
+            output.push_str("\n\n----- COMPILED JAVASCRIPT\n");
+            output.push_str(&compiled);
+
         insta::assert_snapshot!(insta::internals::AutoName, output, $src);
     };
 
diff --git a/compiler-core/src/type_/tests.rs b/compiler-core/src/type_/tests.rs
index 13ad6ca70..1e1375dda 100644
--- a/compiler-core/src/type_/tests.rs
+++ b/compiler-core/src/type_/tests.rs
@@ -90,8 +90,6 @@ macro_rules! assert_module_error {
     };
 
     ($(($name:expr, $module_src:literal)),+, $src:literal $(,)?) => {
-        use std::fmt::Write as _;
-
         let error = $crate::type_::tests::module_error(
             $src,
             vec![
@@ -101,15 +99,20 @@ macro_rules! assert_module_error {
 
         let mut output = String::from("----- SOURCE CODE\n");
         for (name, src) in [$(($name, $module_src)),*] {
-            let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+            output.push_str("-- ");
+            output.push_str(name);
+            output.push_str(".gleam\n");
+            output.push_str(src);
+            output.push_str("\n\n");
         }
-        let _ = write!(output, "-- main.gleam\n{}\n\n----- ERROR\n{error}", $src);
+        output.push_str("-- main.gleam\n");
+        output.push_str($src);
+        output.push_str("\n\n----- ERROR\n");
+        output.push_str(&error);
         insta::assert_snapshot!(insta::internals::AutoName, output, $src);
     };
 
     ($(($package:literal, $name:expr, $module_src:literal)),+, $src:literal $(,)?) => {
-        use std::fmt::Write as _;
-
         let error = $crate::type_::tests::module_error(
             $src,
             vec![
@@ -119,9 +122,16 @@ macro_rules! assert_module_error {
 
         let mut output = String::from("----- SOURCE CODE\n");
         for (name, src) in [$(($name, $module_src)),*] {
-            let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+            output.push_str("-- ");
+            output.push_str(name);
+            output.push_str(".gleam\n");
+            output.push_str(src);
+            output.push_str("\n\n");
         }
-        let _ = write!(output, "-- main.gleam\n{}\n\n----- ERROR\n{error}", $src);
+        output.push_str("-- main.gleam\n");
+        output.push_str($src);
+        output.push_str("\n\n----- ERROR\n");
+        output.push_str(&error);
         insta::assert_snapshot!(insta::internals::AutoName, output, $src);
     };
 }
@@ -235,8 +245,6 @@ macro_rules! assert_warning {
     };
 
     ($(($name:expr, $module_src:literal)),+, $src:literal $(,)?) => {
-        use std::fmt::Write as _;
-
         let warning = $crate::type_::tests::get_printed_warnings(
             $src,
             vec![
@@ -249,15 +257,21 @@ macro_rules! assert_warning {
 
         let mut output = String::from("----- SOURCE CODE\n");
         for (name, src) in [$(($name, $module_src)),*] {
-            let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+            output.push_str("-- ");
+            output.push_str(name);
+            output.push_str(".gleam\n");
+            output.push_str(src);
+            output.push_str("\n\n");
         }
-        let _ = write!(output, "-- main.gleam\n{}\n\n----- WARNING\n{warning}", $src);
+
+        output.push_str("-- main.gleam\n");
+        output.push_str($src);
+        output.push_str("\n\n----- WARNING\n");
+        output.push_str(&warning);
         insta::assert_snapshot!(insta::internals::AutoName, output, $src);
     };
 
     ($(($package:expr, $name:expr, $module_src:literal)),+, $src:expr) => {
-        use std::fmt::Write as _;
-
         let warning = $crate::type_::tests::get_printed_warnings(
             $src,
             vec![$(($package, $name, $module_src)),*],
@@ -268,9 +282,17 @@ macro_rules! assert_warning {
 
         let mut output = String::from("----- SOURCE CODE\n");
         for (name, src) in [$(($name, $module_src)),*] {
-            let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+            output.push_str("-- ");
+            output.push_str(name);
+            output.push_str(".gleam\n");
+            output.push_str(src);
+            output.push_str("\n\n");
         }
-        let _ = write!(output, "-- main.gleam\n{}\n\n----- WARNING\n{warning}", $src);
+
+        output.push_str("-- main.gleam\n");
+        output.push_str($src);
+        output.push_str("\n\n----- WARNING\n");
+        output.push_str(&warning);
         insta::assert_snapshot!(insta::internals::AutoName, output, $src);
     };
 }
diff --git a/compiler-core/src/warning.rs b/compiler-core/src/warning.rs
index 01863f8f3..af2732688 100644
--- a/compiler-core/src/warning.rs
+++ b/compiler-core/src/warning.rs
@@ -22,7 +22,6 @@ use debug_ignore::DebugIgnore;
 use ecow::EcoString;
 use itertools::Itertools;
 use std::{
-    fmt::Write as _,
     io::Write,
     sync::{Arc, atomic::Ordering},
 };
@@ -1102,10 +1101,11 @@ Either change the pattern or use `panic` to unconditionally fail.",
                     let mut text = format!("`{name}` is not a function");
                     match arguments {
                         0 => {
-                            let _ = write!(
-                                text,
-                                ", you can just write `{name}` instead of `{name}()`."
-                            );
+                            text.push_str(", you can just write `");
+                            text.push_str(name);
+                            text.push_str("` instead of `");
+                            text.push_str(name);
+                            text.push_str("()`.");
                         }
                         1 => text.push_str(
                             " and will crash before it can do anything with this argument.",
diff --git a/language-server/src/tests/action.rs b/language-server/src/tests/action.rs
index 4527122c4..c8765342f 100644
--- a/language-server/src/tests/action.rs
+++ b/language-server/src/tests/action.rs
@@ -6,7 +6,6 @@ use lsp_types::{
     CodeActionContext, CodeActionParams, DocumentChange, PartialResultParams, Position, Uri as Url,
     WorkDoneProgressParams,
 };
-use std::fmt::Write as _;
 
 use super::*;
 use crate::path;
@@ -249,7 +248,8 @@ macro_rules! assert_code_action {
         );
 
         if !file_operations.is_empty() {
-            let _ = write!(output, "\n----- FILE OPERATIONS -----\n{file_operations}");
+            output.push_str("\n----- FILE OPERATIONS -----\n");
+            output.push_str(&file_operations);
         }
 
         insta::assert_snapshot!(insta::internals::AutoName, output, src);
diff --git a/language-server/src/tests/document_highlight.rs b/language-server/src/tests/document_highlight.rs
index 3d5590438..73418f0bb 100644
--- a/language-server/src/tests/document_highlight.rs
+++ b/language-server/src/tests/document_highlight.rs
@@ -86,8 +86,6 @@ macro_rules! assert_highlights {
     };
 
     ($project:expr, $position:expr $(,)?) => {
-        use std::fmt::Write as _;
-
         let project = $project;
         let src = project.src;
         let position = $position.find_position(src);
@@ -101,22 +99,24 @@ macro_rules! assert_highlights {
             } else {
                 &Vec::new()
             };
-            let _ = write!(
-                output,
-                "-- {name}.gleam\n{}\n\n",
-                show_highlights(src, None, highlights_in_module)
-            );
+
+            output.push_str("-- ");
+            output.push_str(name);
+            output.push_str(".gleam\n");
+            output.push_str(&show_highlights(src, None, highlights_in_module));
+            output.push_str("\n\n");
         }
         let highlights_in_app_module = if module_name == "app" {
             &result
         } else {
             &Vec::new()
         };
-        let _ = write!(
-            output,
-            "-- app.gleam\n{}",
-            show_highlights(src, Some(position), highlights_in_app_module)
-        );
+        output.push_str("-- app.gleam\n");
+        output.push_str(&show_highlights(
+            src,
+            Some(position),
+            highlights_in_app_module,
+        ));
 
         insta::assert_snapshot!(insta::internals::AutoName, output, src);
     };
diff --git a/language-server/src/tests/reference.rs b/language-server/src/tests/reference.rs
index 3cac0cfb7..6bf23c396 100644
--- a/language-server/src/tests/reference.rs
+++ b/language-server/src/tests/reference.rs
@@ -94,8 +94,6 @@ macro_rules! assert_references {
     };
 
     ($project:expr, $position:expr $(,)?) => {
-        use std::fmt::Write as _;
-
         let project = $project;
         let src = project.src;
         let position = $position.find_position(src);
@@ -103,21 +101,22 @@ macro_rules! assert_references {
 
         let mut output = String::new();
         for (name, src) in project.root_package_modules.iter() {
-            let _ = write!(
-                output,
-                "-- {name}.gleam\n{}\n\n",
-                show_references(src, None, result.get(*name).unwrap_or(&Vec::new()))
-            );
-        }
-        let _ = write!(
-            output,
-            "-- app.gleam\n{}",
-            show_references(
+            output.push_str("-- ");
+            output.push_str(name);
+            output.push_str(".gleam\n");
+            output.push_str(&show_references(
                 src,
-                Some(position),
-                result.get("app").unwrap_or(&Vec::new())
-            )
-        );
+                None,
+                result.get(*name).unwrap_or(&Vec::new()),
+            ));
+            output.push_str("\n\n");
+        }
+        output.push_str("-- app.gleam\n");
+        output.push_str(&show_references(
+            src,
+            Some(position),
+            result.get("app").unwrap_or(&Vec::new()),
+        ));
 
         insta::assert_snapshot!(insta::internals::AutoName, output, src);
     };
diff --git a/language-server/src/tests/rename.rs b/language-server/src/tests/rename.rs
index 853beaf29..5277df479 100644
--- a/language-server/src/tests/rename.rs
+++ b/language-server/src/tests/rename.rs
@@ -2,7 +2,6 @@
 // SPDX-FileCopyrightText: 2025 The Gleam contributors
 
 use std::collections::HashMap;
-use std::fmt::Write as _;
 
 use lsp_types::{
     Position, PrepareRenameParams, PrepareRenamePlaceholder, Range, RenameParams,
@@ -120,7 +119,11 @@ fn display_result(
 ) -> String {
     let mut output = String::from("----- BEFORE RENAME\n");
     for (name, src) in project.root_package_modules.iter() {
-        let _ = write!(output, "-- {name}.gleam\n{src}\n\n");
+        output.push_str("-- ");
+        output.push_str(name);
+        output.push_str(".gleam\n");
+        output.push_str(src);
+        output.push_str("\n\n");
     }
 
     let src = project.src;
@@ -129,10 +132,9 @@ fn display_result(
     } else {
         src.to_string()
     };
-    let _ = write!(
-        output,
-        "-- app.gleam\n{app_src_before}\n\n----- AFTER RENAME\n",
-    );
+    output.push_str("-- app.gleam\n");
+    output.push_str(&app_src_before);
+    output.push_str("\n\n----- AFTER RENAME\n");
 
     for &(name, src) in project.root_package_modules.iter() {
         let used_name = if let Some(new_name) = renamed_modules.get(name) {
@@ -140,22 +142,24 @@ fn display_result(
         } else {
             name
         };
-        let _ = write!(
-            output,
-            "-- {used_name}.gleam\n{}\n\n",
+
+        output.push_str("-- ");
+        output.push_str(used_name);
+        output.push_str(".gleam\n");
+        output.push_str(
             modules
                 .get(name)
                 .map(|string| string.as_str())
-                .unwrap_or(src)
+                .unwrap_or(src),
         );
+        output.push_str("\n\n");
     }
-    let _ = write!(
-        output,
-        "-- app.gleam\n{}",
+    output.push_str("-- app.gleam\n");
+    output.push_str(
         modules
             .get("app")
             .map(|string| string.as_str())
-            .unwrap_or(src)
+            .unwrap_or(src),
     );
     output
 }
diff --git a/test-package-compiler/build.rs b/test-package-compiler/build.rs
index 633f50e46..4877071ab 100644
--- a/test-package-compiler/build.rs
+++ b/test-package-compiler/build.rs
@@ -1,7 +1,6 @@
 // SPDX-License-Identifier: Apache-2.0
 // SPDX-FileCopyrightText: 2022 The Gleam contributors
 
-use std::fmt::Write as _;
 use std::path::PathBuf;
 
 pub fn main() {
@@ -26,20 +25,33 @@ pub fn main() {
     for name in names {
         let path = cases.join(&name);
         let path = path.to_str().unwrap().replace('\\', "/");
-        let _ = write!(
-            module,
-            r#"
+        module.push_str(
+            "
 #[rustfmt::skip]
 #[test]
-fn {name}() {{
-    let output = crate::prepare("{path}");
+fn ",
+        );
+        module.push_str(&name);
+        module.push_str("() {\n");
+        module.push_str("    let output = crate::prepare(\"");
+        module.push_str(&path);
+        module.push_str(
+            "\");
     insta::assert_snapshot!(
-        "{name}",
+        \"",
+        );
+        module.push_str(&name);
+        module.push_str(
+            "\",
         output,
-        "{path}",
+        \"",
+        );
+        module.push_str(&path);
+        module.push_str(
+            "\",
     );
-}}
-"#
+}
+",
         );
     }