diff --git a/lib/filetests/src/test_compile.rs b/lib/filetests/src/test_compile.rs
index 8cb26b4f1f..73f178b9b7 100644
--- a/lib/filetests/src/test_compile.rs
+++ b/lib/filetests/src/test_compile.rs
@@ -7,7 +7,6 @@ use cretonne_codegen::print_errors::pretty_error;
 use cretonne_codegen::{binemit, ir};
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestCompile;
@@ -64,8 +63,7 @@ impl SubTest for TestCompile {
         }
 
         // Run final code through filecheck.
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func.display(Some(isa))).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.display(Some(isa)).to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_dce.rs b/lib/filetests/src/test_dce.rs
index 38e2b907a9..4c795b5a2e 100644
--- a/lib/filetests/src/test_dce.rs
+++ b/lib/filetests/src/test_dce.rs
@@ -10,7 +10,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestDCE;
@@ -42,8 +41,7 @@ impl SubTest for TestDCE {
             .dce(context.flags_or_isa())
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_legalizer.rs b/lib/filetests/src/test_legalizer.rs
index 8ce1cffb1b..afaaf3fdcb 100644
--- a/lib/filetests/src/test_legalizer.rs
+++ b/lib/filetests/src/test_legalizer.rs
@@ -8,7 +8,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestLegalizer;
@@ -44,8 +43,7 @@ impl SubTest for TestLegalizer {
             .legalize(isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, e))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func.display(Some(isa))).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.display(Some(isa)).to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_licm.rs b/lib/filetests/src/test_licm.rs
index 2dda7b976b..9f42254a18 100644
--- a/lib/filetests/src/test_licm.rs
+++ b/lib/filetests/src/test_licm.rs
@@ -10,7 +10,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestLICM;
@@ -42,8 +41,7 @@ impl SubTest for TestLICM {
             .licm(context.flags_or_isa())
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_postopt.rs b/lib/filetests/src/test_postopt.rs
index 72bc3dfc2f..6e3712922f 100644
--- a/lib/filetests/src/test_postopt.rs
+++ b/lib/filetests/src/test_postopt.rs
@@ -7,7 +7,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestPostopt;
@@ -39,8 +38,7 @@ impl SubTest for TestPostopt {
             .postopt(isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_preopt.rs b/lib/filetests/src/test_preopt.rs
index 1a3131ba83..ad68e59c09 100644
--- a/lib/filetests/src/test_preopt.rs
+++ b/lib/filetests/src/test_preopt.rs
@@ -7,7 +7,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestPreopt;
@@ -39,8 +38,7 @@ impl SubTest for TestPreopt {
             .preopt(isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func).map_err(|e| e.to_string())?;
+        let text = &comp_ctx.func.to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_regalloc.rs b/lib/filetests/src/test_regalloc.rs
index c74662c19a..b592cd12dc 100644
--- a/lib/filetests/src/test_regalloc.rs
+++ b/lib/filetests/src/test_regalloc.rs
@@ -10,7 +10,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestRegalloc;
@@ -51,8 +50,7 @@ impl SubTest for TestRegalloc {
             .regalloc(isa)
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, e))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func.display(Some(isa))).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.display(Some(isa)).to_string();
         run_filecheck(&text, context)
     }
 }
diff --git a/lib/filetests/src/test_simple_gvn.rs b/lib/filetests/src/test_simple_gvn.rs
index 7def78e95a..a78d30753c 100644
--- a/lib/filetests/src/test_simple_gvn.rs
+++ b/lib/filetests/src/test_simple_gvn.rs
@@ -10,7 +10,6 @@ use cretonne_codegen::ir::Function;
 use cretonne_codegen::print_errors::pretty_error;
 use cretonne_reader::TestCommand;
 use std::borrow::Cow;
-use std::fmt::Write;
 use subtest::{run_filecheck, Context, Result, SubTest};
 
 struct TestSimpleGVN;
@@ -41,8 +40,7 @@ impl SubTest for TestSimpleGVN {
             .simple_gvn(context.flags_or_isa())
             .map_err(|e| pretty_error(&comp_ctx.func, context.isa, Into::into(e)))?;
 
-        let mut text = String::new();
-        write!(&mut text, "{}", &comp_ctx.func).map_err(|e| e.to_string())?;
+        let text = comp_ctx.func.to_string();
         run_filecheck(&text, context)
     }
 }