From f095e19c2c9d097107b434fc6156987884e5251b Mon Sep 17 00:00:00 2001
From: Micha Reiser <micha@reiser.io>
Date: Fri, 12 Dec 2025 08:37:57 +0100
Subject: [PATCH] Use datatest for formatter tests

---
 Cargo.lock                                    |  53 ++-
 Cargo.toml                                    |   1 +
 crates/ruff_python_formatter/Cargo.toml       |   5 +-
 .../ruff_python_formatter/tests/fixtures.rs   | 427 ++++++++----------
 4 files changed, 256 insertions(+), 230 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index e75eedb6c2..a746fa1af0 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -254,6 +254,21 @@ dependencies = [
  "syn",
 ]
 
+[[package]]
+name = "bit-set"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08807e080ed7f9d5433fa9b275196cfc35414f66a0c79d864dc51a0d825231a3"
+dependencies = [
+ "bit-vec",
+]
+
+[[package]]
+name = "bit-vec"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e764a1d40d510daf35e07be9eb06e75770908c27d411ee6c92109c9840eaaf7"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -944,6 +959,18 @@ dependencies = [
  "parking_lot_core",
 ]
 
+[[package]]
+name = "datatest-stable"
+version = "0.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a867d7322eb69cf3a68a5426387a25b45cb3b9c5ee41023ee6cea92e2afadd82"
+dependencies = [
+ "camino",
+ "fancy-regex",
+ "libtest-mimic 0.8.1",
+ "walkdir",
+]
+
 [[package]]
 name = "derive-where"
 version = "1.6.0"
@@ -1138,6 +1165,17 @@ dependencies = [
  "windows-sys 0.61.0",
 ]
 
+[[package]]
+name = "fancy-regex"
+version = "0.14.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6e24cb5a94bcae1e5408b0effca5cd7172ea3c5755049c5f3af4cd283a165298"
+dependencies = [
+ "bit-set",
+ "regex-automata",
+ "regex-syntax",
+]
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"
@@ -1919,6 +1957,18 @@ dependencies = [
  "threadpool",
 ]
 
+[[package]]
+name = "libtest-mimic"
+version = "0.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5297962ef19edda4ce33aaa484386e0a5b3d7f2f4e037cbeee00503ef6b29d33"
+dependencies = [
+ "anstream",
+ "anstyle",
+ "clap",
+ "escape8259",
+]
+
 [[package]]
 name = "linux-raw-sys"
 version = "0.11.0"
@@ -3278,6 +3328,7 @@ dependencies = [
  "anyhow",
  "clap",
  "countme",
+ "datatest-stable",
  "insta",
  "itertools 0.14.0",
  "memchr",
@@ -4311,7 +4362,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5fe242ee9e646acec9ab73a5c540e8543ed1b107f0ce42be831e0775d423c396"
 dependencies = [
  "ignore",
- "libtest-mimic",
+ "libtest-mimic 0.7.3",
  "snapbox",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index 0badc79e3c..dbd9808fdd 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -81,6 +81,7 @@ compact_str = "0.9.0"
 criterion = { version = "0.7.0", default-features = false }
 crossbeam = { version = "0.8.4" }
 dashmap = { version = "6.0.1" }
+datatest-stable = { version = "0.3.3" }
 dir-test = { version = "0.4.0" }
 dunce = { version = "1.0.5" }
 drop_bomb = { version = "0.1.5" }
diff --git a/crates/ruff_python_formatter/Cargo.toml b/crates/ruff_python_formatter/Cargo.toml
index 95ca60ee10..2cb61fdc56 100644
--- a/crates/ruff_python_formatter/Cargo.toml
+++ b/crates/ruff_python_formatter/Cargo.toml
@@ -43,6 +43,7 @@ tracing = { workspace = true }
 [dev-dependencies]
 ruff_formatter = { workspace = true }
 
+datatest-stable = { workspace = true }
 insta = { workspace = true, features = ["glob"] }
 regex = { workspace = true }
 serde = { workspace = true }
@@ -54,8 +55,8 @@ similar = { workspace = true }
 ignored = ["ruff_cache"]
 
 [[test]]
-name = "ruff_python_formatter_fixtures"
-path = "tests/fixtures.rs"
+name = "fixtures"
+harness = false
 test = true
 required-features = ["serde"]
 
diff --git a/crates/ruff_python_formatter/tests/fixtures.rs b/crates/ruff_python_formatter/tests/fixtures.rs
index 33741bd744..d75a42c569 100644
--- a/crates/ruff_python_formatter/tests/fixtures.rs
+++ b/crates/ruff_python_formatter/tests/fixtures.rs
@@ -1,4 +1,7 @@
 use crate::normalizer::Normalizer;
+use anyhow::anyhow;
+use datatest_stable::Utf8Path;
+use insta::assert_snapshot;
 use ruff_db::diagnostic::{
     Annotation, Diagnostic, DiagnosticFormat, DiagnosticId, DisplayDiagnosticConfig,
     DisplayDiagnostics, DummyFileResolver, Severity, Span, SubDiagnostic, SubDiagnosticSeverity,
@@ -24,26 +27,27 @@ use std::{fmt, fs};
 
 mod normalizer;
 
-#[test]
-fn black_compatibility() {
-    let test_file = |input_path: &Path| {
-        let content = fs::read_to_string(input_path).unwrap();
+#[expect(clippy::needless_pass_by_value)]
+fn black_compatibility(input_path: &Utf8Path, content: String) -> datatest_stable::Result<()> {
+    let test_name = input_path
+        .strip_prefix("./resources/test/fixtures/black")
+        .unwrap_or(input_path)
+        .as_str();
 
-        let options_path = input_path.with_extension("options.json");
+    let options_path = input_path.with_extension("options.json");
 
-        let options: PyFormatOptions = if let Ok(options_file) = fs::File::open(&options_path) {
-            let reader = BufReader::new(options_file);
-            serde_json::from_reader(reader).unwrap_or_else(|_| {
-                panic!("Expected option file {options_path:?} to be a valid Json file")
-            })
-        } else {
-            PyFormatOptions::from_extension(input_path)
-        };
+    let options: PyFormatOptions = if let Ok(options_file) = fs::File::open(&options_path) {
+        let reader = BufReader::new(options_file);
+        serde_json::from_reader(reader).map_err(|err| {
+            anyhow!("Expected option file {options_path:?} to be a valid Json file: {err}")
+        })?
+    } else {
+        PyFormatOptions::from_extension(input_path.as_std_path())
+    };
 
-        let first_line = content.lines().next().unwrap_or_default();
-        let formatted_code = if first_line.starts_with("# flags:")
-            && first_line.contains("--line-ranges=")
-        {
+    let first_line = content.lines().next().unwrap_or_default();
+    let formatted_code =
+        if first_line.starts_with("# flags:") && first_line.contains("--line-ranges=") {
             let line_index = LineIndex::from_source_text(&content);
 
             let ranges = first_line
@@ -69,13 +73,9 @@ fn black_compatibility() {
             let mut formatted_code = content.clone();
 
             for range in ranges {
-                let formatted =
-                    format_range(&content, range, options.clone()).unwrap_or_else(|err| {
-                        panic!(
-                            "Range-formatting of {} to succeed but encountered error {err}",
-                            input_path.display()
-                        )
-                    });
+                let formatted = format_range(&content, range, options.clone()).map_err(|err| {
+                    anyhow!("Range-formatting to succeed but encountered error {err}")
+                })?;
 
                 let range = formatted.source_range();
 
@@ -86,12 +86,8 @@ fn black_compatibility() {
 
             formatted_code
         } else {
-            let printed = format_module_source(&content, options.clone()).unwrap_or_else(|err| {
-                panic!(
-                    "Formatting of {} to succeed but encountered error {err}",
-                    input_path.display()
-                )
-            });
+            let printed = format_module_source(&content, options.clone())
+                .map_err(|err| anyhow!("Formatting to succeed but encountered error {err}"))?;
 
             let formatted_code = printed.into_code();
 
@@ -100,191 +96,133 @@ fn black_compatibility() {
             formatted_code
         };
 
-        let extension = input_path
-            .extension()
-            .expect("Test file to have py or pyi extension")
-            .to_string_lossy();
-        let expected_path = input_path.with_extension(format!("{extension}.expect"));
-        let expected_output = fs::read_to_string(&expected_path)
-            .unwrap_or_else(|_| panic!("Expected Black output file '{expected_path:?}' to exist"));
+    let extension = input_path
+        .extension()
+        .expect("Test file to have py or pyi extension");
+    let expected_path = input_path.with_extension(format!("{extension}.expect"));
+    let expected_output = fs::read_to_string(&expected_path)
+        .unwrap_or_else(|_| panic!("Expected Black output file '{expected_path:?}' to exist"));
 
-        let unsupported_syntax_errors =
-            ensure_unchanged_ast(&content, &formatted_code, &options, input_path);
+    let unsupported_syntax_errors =
+        ensure_unchanged_ast(&content, &formatted_code, &options, input_path);
 
-        if formatted_code == expected_output {
-            // Black and Ruff formatting matches. Delete any existing snapshot files because the Black output
-            // already perfectly captures the expected output.
-            // The following code mimics insta's logic generating the snapshot name for a test.
-            let workspace_path = std::env::var("CARGO_MANIFEST_DIR").unwrap();
+    // Black and Ruff formatting matches. Delete any existing snapshot files because the Black output
+    // already perfectly captures the expected output.
+    // The following code mimics insta's logic generating the snapshot name for a test.
+    let workspace_path = std::env::var("CARGO_MANIFEST_DIR").unwrap();
 
-            let mut components = input_path.components().rev();
-            let file_name = components.next().unwrap();
-            let test_suite = components.next().unwrap();
+    let full_snapshot_name = format!("black_compatibility@{test_name}.snap",);
 
-            let snapshot_name = format!(
-                "black_compatibility@{}__{}.snap",
-                test_suite.as_os_str().to_string_lossy(),
-                file_name.as_os_str().to_string_lossy()
-            );
+    let snapshot_path = Path::new(&workspace_path)
+        .join("tests/snapshots")
+        .join(full_snapshot_name);
 
-            let snapshot_path = Path::new(&workspace_path)
-                .join("tests/snapshots")
-                .join(snapshot_name);
-            if snapshot_path.exists() && snapshot_path.is_file() {
-                // SAFETY: This is a convenience feature. That's why we don't want to abort
-                // when deleting a no longer needed snapshot fails.
-                fs::remove_file(&snapshot_path).ok();
-            }
-
-            let new_snapshot_path = snapshot_path.with_extension("snap.new");
-            if new_snapshot_path.exists() && new_snapshot_path.is_file() {
-                // SAFETY: This is a convenience feature. That's why we don't want to abort
-                // when deleting a no longer needed snapshot fails.
-                fs::remove_file(&new_snapshot_path).ok();
-            }
-        } else {
-            // Black and Ruff have different formatting. Write out a snapshot that covers the differences
-            // today.
-            let mut snapshot = String::new();
-            write!(snapshot, "{}", Header::new("Input")).unwrap();
-            write!(snapshot, "{}", CodeFrame::new("python", &content)).unwrap();
-
-            write!(snapshot, "{}", Header::new("Black Differences")).unwrap();
-
-            let diff = TextDiff::from_lines(expected_output.as_str(), &formatted_code)
-                .unified_diff()
-                .header("Black", "Ruff")
-                .to_string();
-
-            write!(snapshot, "{}", CodeFrame::new("diff", &diff)).unwrap();
-
-            write!(snapshot, "{}", Header::new("Ruff Output")).unwrap();
-            write!(snapshot, "{}", CodeFrame::new("python", &formatted_code)).unwrap();
-
-            write!(snapshot, "{}", Header::new("Black Output")).unwrap();
-            write!(snapshot, "{}", CodeFrame::new("python", &expected_output)).unwrap();
-
-            if !unsupported_syntax_errors.is_empty() {
-                write!(snapshot, "{}", Header::new("New Unsupported Syntax Errors")).unwrap();
-                writeln!(
-                    snapshot,
-                    "{}",
-                    DisplayDiagnostics::new(
-                        &DummyFileResolver,
-                        &DisplayDiagnosticConfig::default().format(DiagnosticFormat::Full),
-                        &unsupported_syntax_errors
-                    )
-                )
-                .unwrap();
-            }
-
-            insta::with_settings!({
-                omit_expression => true,
-                input_file => input_path,
-                prepend_module_to_snapshot => false,
-            }, {
-                insta::assert_snapshot!(snapshot);
-            });
+    if formatted_code == expected_output {
+        if snapshot_path.exists() && snapshot_path.is_file() {
+            // SAFETY: This is a convenience feature. That's why we don't want to abort
+            // when deleting a no longer needed snapshot fails.
+            fs::remove_file(&snapshot_path).ok();
         }
-    };
 
-    insta::glob!(
-        "../resources",
-        "test/fixtures/black/**/*.{py,pyi}",
-        test_file
-    );
+        let new_snapshot_path = snapshot_path.with_extension("snap.new");
+        if new_snapshot_path.exists() && new_snapshot_path.is_file() {
+            // SAFETY: This is a convenience feature. That's why we don't want to abort
+            // when deleting a no longer needed snapshot fails.
+            fs::remove_file(&new_snapshot_path).ok();
+        }
+    } else {
+        // Black and Ruff have different formatting. Write out a snapshot that covers the differences
+        // today.
+        let mut snapshot = String::new();
+        write!(snapshot, "{}", Header::new("Input")).unwrap();
+        write!(snapshot, "{}", CodeFrame::new("python", &content)).unwrap();
+
+        write!(snapshot, "{}", Header::new("Black Differences")).unwrap();
+
+        let diff = TextDiff::from_lines(expected_output.as_str(), &formatted_code)
+            .unified_diff()
+            .header("Black", "Ruff")
+            .to_string();
+
+        write!(snapshot, "{}", CodeFrame::new("diff", &diff)).unwrap();
+
+        write!(snapshot, "{}", Header::new("Ruff Output")).unwrap();
+        write!(snapshot, "{}", CodeFrame::new("python", &formatted_code)).unwrap();
+
+        write!(snapshot, "{}", Header::new("Black Output")).unwrap();
+        write!(snapshot, "{}", CodeFrame::new("python", &expected_output)).unwrap();
+
+        if !unsupported_syntax_errors.is_empty() {
+            write!(snapshot, "{}", Header::new("New Unsupported Syntax Errors")).unwrap();
+            writeln!(
+                snapshot,
+                "{}",
+                DisplayDiagnostics::new(
+                    &DummyFileResolver,
+                    &DisplayDiagnosticConfig::default().format(DiagnosticFormat::Full),
+                    &unsupported_syntax_errors
+                )
+            )
+            .unwrap();
+        }
+
+        let mut settings = insta::Settings::clone_current();
+        settings.set_omit_expression(true);
+        settings.set_input_file(input_path);
+        settings.set_prepend_module_to_snapshot(false);
+        settings.set_snapshot_suffix(test_name);
+        let _settings = settings.bind_to_scope();
+
+        assert_snapshot!(snapshot);
+    }
+    Ok(())
 }
 
-#[test]
-fn format() {
-    let test_file = |input_path: &Path| {
-        let content = fs::read_to_string(input_path).unwrap();
+#[expect(clippy::needless_pass_by_value)]
+fn format(input_path: &Utf8Path, content: String) -> datatest_stable::Result<()> {
+    let test_name = input_path
+        .strip_prefix("./resources/test/fixtures/ruff")
+        .unwrap_or(input_path)
+        .as_str();
 
-        let mut snapshot = format!("## Input\n{}", CodeFrame::new("python", &content));
-        let options_path = input_path.with_extension("options.json");
+    let mut snapshot = format!("## Input\n{}", CodeFrame::new("python", &content));
+    let options_path = input_path.with_extension("options.json");
 
-        if let Ok(options_file) = fs::File::open(&options_path) {
-            let reader = BufReader::new(options_file);
-            let options: Vec<PyFormatOptions> =
-                serde_json::from_reader(reader).unwrap_or_else(|_| {
-                    panic!("Expected option file {options_path:?} to be a valid Json file")
-                });
+    if let Ok(options_file) = fs::File::open(&options_path) {
+        let reader = BufReader::new(options_file);
+        let options: Vec<PyFormatOptions> = serde_json::from_reader(reader).map_err(|_| {
+            anyhow!("Expected option file {options_path:?} to be a valid Json file")
+        })?;
 
-            writeln!(snapshot, "## Outputs").unwrap();
+        writeln!(snapshot, "## Outputs").unwrap();
 
-            for (i, options) in options.into_iter().enumerate() {
-                let (formatted_code, unsupported_syntax_errors) =
-                    format_file(&content, &options, input_path);
-
-                writeln!(
-                    snapshot,
-                    "### Output {}\n{}{}",
-                    i + 1,
-                    CodeFrame::new("", &DisplayPyOptions(&options)),
-                    CodeFrame::new("python", &formatted_code)
-                )
-                .unwrap();
-
-                if options.preview().is_enabled() {
-                    continue;
-                }
-
-                // We want to capture the differences in the preview style in our fixtures
-                let options_preview = options.with_preview(PreviewMode::Enabled);
-                let (formatted_preview, _) = format_file(&content, &options_preview, input_path);
-
-                if formatted_code != formatted_preview {
-                    // Having both snapshots makes it hard to see the difference, so we're keeping only
-                    // diff.
-                    writeln!(
-                        snapshot,
-                        "#### Preview changes\n{}",
-                        CodeFrame::new(
-                            "diff",
-                            TextDiff::from_lines(&formatted_code, &formatted_preview)
-                                .unified_diff()
-                                .header("Stable", "Preview")
-                        )
-                    )
-                    .unwrap();
-                }
-
-                if !unsupported_syntax_errors.is_empty() {
-                    writeln!(
-                        snapshot,
-                        "### Unsupported Syntax Errors\n{}",
-                        DisplayDiagnostics::new(
-                            &DummyFileResolver,
-                            &DisplayDiagnosticConfig::default().format(DiagnosticFormat::Full),
-                            &unsupported_syntax_errors
-                        )
-                    )
-                    .unwrap();
-                }
-            }
-        } else {
-            // We want to capture the differences in the preview style in our fixtures
-            let options = PyFormatOptions::from_extension(input_path);
+        for (i, options) in options.into_iter().enumerate() {
             let (formatted_code, unsupported_syntax_errors) =
                 format_file(&content, &options, input_path);
 
+            writeln!(
+                snapshot,
+                "### Output {}\n{}{}",
+                i + 1,
+                CodeFrame::new("", &DisplayPyOptions(&options)),
+                CodeFrame::new("python", &formatted_code)
+            )
+            .unwrap();
+
+            if options.preview().is_enabled() {
+                continue;
+            }
+
+            // We want to capture the differences in the preview style in our fixtures
             let options_preview = options.with_preview(PreviewMode::Enabled);
             let (formatted_preview, _) = format_file(&content, &options_preview, input_path);
 
-            if formatted_code == formatted_preview {
-                writeln!(
-                    snapshot,
-                    "## Output\n{}",
-                    CodeFrame::new("python", &formatted_code)
-                )
-                .unwrap();
-            } else {
+            if formatted_code != formatted_preview {
                 // Having both snapshots makes it hard to see the difference, so we're keeping only
                 // diff.
                 writeln!(
                     snapshot,
-                    "## Output\n{}\n## Preview changes\n{}",
-                    CodeFrame::new("python", &formatted_code),
+                    "#### Preview changes\n{}",
                     CodeFrame::new(
                         "diff",
                         TextDiff::from_lines(&formatted_code, &formatted_preview)
@@ -298,7 +236,7 @@ fn format() {
             if !unsupported_syntax_errors.is_empty() {
                 writeln!(
                     snapshot,
-                    "## Unsupported Syntax Errors\n{}",
+                    "### Unsupported Syntax Errors\n{}",
                     DisplayDiagnostics::new(
                         &DummyFileResolver,
                         &DisplayDiagnosticConfig::default().format(DiagnosticFormat::Full),
@@ -308,27 +246,74 @@ fn format() {
                 .unwrap();
             }
         }
+    } else {
+        // We want to capture the differences in the preview style in our fixtures
+        let options = PyFormatOptions::from_extension(input_path.as_std_path());
+        let (formatted_code, unsupported_syntax_errors) =
+            format_file(&content, &options, input_path);
 
-        insta::with_settings!({
-            omit_expression => true,
-            input_file => input_path,
-            prepend_module_to_snapshot => false,
-        }, {
-            insta::assert_snapshot!(snapshot);
-        });
-    };
+        let options_preview = options.with_preview(PreviewMode::Enabled);
+        let (formatted_preview, _) = format_file(&content, &options_preview, input_path);
 
-    insta::glob!(
-        "../resources",
-        "test/fixtures/ruff/**/*.{py,pyi}",
-        test_file
-    );
+        if formatted_code == formatted_preview {
+            writeln!(
+                snapshot,
+                "## Output\n{}",
+                CodeFrame::new("python", &formatted_code)
+            )
+            .unwrap();
+        } else {
+            // Having both snapshots makes it hard to see the difference, so we're keeping only
+            // diff.
+            writeln!(
+                snapshot,
+                "## Output\n{}\n## Preview changes\n{}",
+                CodeFrame::new("python", &formatted_code),
+                CodeFrame::new(
+                    "diff",
+                    TextDiff::from_lines(&formatted_code, &formatted_preview)
+                        .unified_diff()
+                        .header("Stable", "Preview")
+                )
+            )
+            .unwrap();
+        }
+
+        if !unsupported_syntax_errors.is_empty() {
+            writeln!(
+                snapshot,
+                "## Unsupported Syntax Errors\n{}",
+                DisplayDiagnostics::new(
+                    &DummyFileResolver,
+                    &DisplayDiagnosticConfig::default().format(DiagnosticFormat::Full),
+                    &unsupported_syntax_errors
+                )
+            )
+            .unwrap();
+        }
+    }
+
+    let mut settings = insta::Settings::clone_current();
+    settings.set_omit_expression(true);
+    settings.set_input_file(input_path);
+    settings.set_prepend_module_to_snapshot(false);
+    settings.set_snapshot_suffix(test_name);
+    let _settings = settings.bind_to_scope();
+
+    assert_snapshot!(snapshot);
+
+    Ok(())
+}
+
+datatest_stable::harness! {
+    { test = black_compatibility, root = "./resources/test/fixtures/black", pattern = r".+\.pyi?$" },
+    { test = format, root="./resources/test/fixtures/ruff", pattern = r".+\.pyi?$" }
 }
 
 fn format_file(
     source: &str,
     options: &PyFormatOptions,
-    input_path: &Path,
+    input_path: &Utf8Path,
 ) -> (String, Vec<Diagnostic>) {
     let (unformatted, formatted_code) = if source.contains("<RANGE_START>") {
         let mut content = source.to_string();
@@ -363,8 +348,7 @@ fn format_file(
             let formatted =
                 format_range(&format_input, range, options.clone()).unwrap_or_else(|err| {
                     panic!(
-                        "Range-formatting of {} to succeed but encountered error {err}",
-                        input_path.display()
+                        "Range-formatting of {input_path} to succeed but encountered error {err}",
                     )
                 });
 
@@ -377,10 +361,7 @@ fn format_file(
         (Cow::Owned(without_markers), content)
     } else {
         let printed = format_module_source(source, options.clone()).unwrap_or_else(|err| {
-            panic!(
-                "Formatting `{input_path} was expected to succeed but it failed: {err}",
-                input_path = input_path.display()
-            )
+            panic!("Formatting `{input_path} was expected to succeed but it failed: {err}",)
         });
         let formatted_code = printed.into_code();
 
@@ -399,22 +380,20 @@ fn format_file(
 fn ensure_stability_when_formatting_twice(
     formatted_code: &str,
     options: &PyFormatOptions,
-    input_path: &Path,
+    input_path: &Utf8Path,
 ) {
     let reformatted = match format_module_source(formatted_code, options.clone()) {
         Ok(reformatted) => reformatted,
         Err(err) => {
             let mut diag = Diagnostic::from(&err);
             if let Some(range) = err.range() {
-                let file =
-                    SourceFileBuilder::new(input_path.to_string_lossy(), formatted_code).finish();
+                let file = SourceFileBuilder::new(input_path.as_str(), formatted_code).finish();
                 let span = Span::from(file).with_range(range);
                 diag.annotate(Annotation::primary(span));
             }
             panic!(
-                "Expected formatted code of {} to be valid syntax: {err}:\
+                "Expected formatted code of {input_path} to be valid syntax: {err}:\
                     \n---\n{formatted_code}---\n{}",
-                input_path.display(),
                 diag.display(&DummyFileResolver, &DisplayDiagnosticConfig::default()),
             );
         }
@@ -440,7 +419,6 @@ Formatted once:
 Formatted twice:
 ---
 {reformatted}---"#,
-            input_path = input_path.display(),
             options = &DisplayPyOptions(options),
             reformatted = reformatted.as_code(),
         );
@@ -467,7 +445,7 @@ fn ensure_unchanged_ast(
     unformatted_code: &str,
     formatted_code: &str,
     options: &PyFormatOptions,
-    input_path: &Path,
+    input_path: &Utf8Path,
 ) -> Vec<Diagnostic> {
     let source_type = options.source_type();
 
@@ -499,11 +477,7 @@ fn ensure_unchanged_ast(
     formatted_unsupported_syntax_errors
         .retain(|fingerprint, _| !unformatted_unsupported_syntax_errors.contains_key(fingerprint));
 
-    let file = SourceFileBuilder::new(
-        input_path.file_name().unwrap().to_string_lossy(),
-        formatted_code,
-    )
-    .finish();
+    let file = SourceFileBuilder::new(input_path.file_name().unwrap(), formatted_code).finish();
     let diagnostics = formatted_unsupported_syntax_errors
         .values()
         .map(|error| {
@@ -533,11 +507,10 @@ fn ensure_unchanged_ast(
         .header("Unformatted", "Formatted")
         .to_string();
         panic!(
-            r#"Reformatting the unformatted code of {} resulted in AST changes.
+            r#"Reformatting the unformatted code of {input_path} resulted in AST changes.
 ---
 {diff}
 "#,
-            input_path.display(),
         );
     }