diff --git a/crates/oxc_linter/src/service/mod.rs b/crates/oxc_linter/src/service/mod.rs
index 15e5fb328d1c2..7ebb9fdca505c 100644
--- a/crates/oxc_linter/src/service/mod.rs
+++ b/crates/oxc_linter/src/service/mod.rs
@@ -6,6 +6,7 @@ use std::{
 
 use oxc_diagnostics::DiagnosticSender;
 use runtime::Runtime;
+pub use runtime::RuntimeFileSystem;
 
 use crate::Linter;
 
@@ -74,10 +75,13 @@ impl LintService {
         Self { runtime }
     }
 
-    #[cfg(test)]
-    pub(crate) fn from_linter(linter: Linter, options: LintServiceOptions) -> Self {
-        let runtime = Runtime::new(linter, options);
-        Self { runtime }
+    #[must_use]
+    pub fn with_file_system(
+        mut self,
+        file_system: Box<dyn RuntimeFileSystem + Sync + Send>,
+    ) -> Self {
+        self.runtime = self.runtime.with_file_system(file_system);
+        self
     }
 
     pub fn linter(&self) -> &Linter {
@@ -105,10 +109,9 @@ impl LintService {
     pub(crate) fn run_test_source<'a>(
         &mut self,
         allocator: &'a oxc_allocator::Allocator,
-        source_text: &str,
         check_syntax_errors: bool,
         tx_error: &DiagnosticSender,
     ) -> Vec<crate::Message<'a>> {
-        self.runtime.run_test_source(allocator, source_text, check_syntax_errors, tx_error)
+        self.runtime.run_test_source(allocator, check_syntax_errors, tx_error)
     }
 }
diff --git a/crates/oxc_linter/src/service/runtime.rs b/crates/oxc_linter/src/service/runtime.rs
index 85793f4b45e15..b04cf8b5424ee 100644
--- a/crates/oxc_linter/src/service/runtime.rs
+++ b/crates/oxc_linter/src/service/runtime.rs
@@ -51,9 +51,6 @@ pub struct Runtime {
     // This is required to support `run: "onType"` configuration
     #[cfg(feature = "language_server")]
     source_text_cache: FxHashMap<Arc<OsStr>, String>,
-
-    #[cfg(test)]
-    pub(super) test_source: std::sync::RwLock<Option<String>>,
 }
 
 /// Output of `Runtime::process_path`
@@ -184,12 +181,9 @@ impl Runtime {
             file_system: Box::new(OsFileSystem),
             #[cfg(feature = "language_server")]
             source_text_cache: FxHashMap::default(),
-            #[cfg(test)]
-            test_source: std::sync::RwLock::new(None),
         }
     }
 
-    #[expect(dead_code)]
     pub fn with_file_system(
         mut self,
         file_system: Box<dyn RuntimeFileSystem + Sync + Send>,
@@ -236,13 +230,6 @@ impl Runtime {
         }
         let source_type = source_type.unwrap_or_default();
 
-        #[cfg(test)]
-        if let (true, Some(test_source)) =
-            (self.paths.contains(path.as_os_str()), &*self.test_source.read().unwrap())
-        {
-            return Some(Ok((source_type, test_source.clone())));
-        }
-
         // The language server uses more up to date source_text provided by `workspace/didChange` request.
         // This is required to support `run: "onType"` configuration
         #[cfg(feature = "language_server")]
@@ -697,15 +684,12 @@ impl Runtime {
     pub(super) fn run_test_source<'a>(
         &mut self,
         allocator: &'a Allocator,
-        source_text: &str,
         check_syntax_errors: bool,
         tx_error: &DiagnosticSender,
     ) -> Vec<Message<'a>> {
         use oxc_allocator::CloneIn;
         use std::sync::Mutex;
 
-        *self.test_source.write().unwrap() = Some(source_text.to_owned());
-
         let messages = Mutex::new(Vec::<Message<'a>>::new());
         rayon::scope(|scope| {
             self.resolve_modules(scope, check_syntax_errors, tx_error, |me, mut module| {
diff --git a/crates/oxc_linter/src/tester.rs b/crates/oxc_linter/src/tester.rs
index 3a9d1fd71d0ea..83275a921e94a 100644
--- a/crates/oxc_linter/src/tester.rs
+++ b/crates/oxc_linter/src/tester.rs
@@ -17,7 +17,9 @@ use crate::{
     Oxlintrc, RuleEnum, RuleWithSeverity,
     fixer::{FixKind, Fixer},
     options::LintOptions,
+    read_to_string,
     rules::RULES,
+    service::RuntimeFileSystem,
 };
 
 #[derive(Eq, PartialEq)]
@@ -165,6 +167,31 @@ where
     }
 }
 
+struct TesterFileSystem {
+    path_to_lint: PathBuf,
+    source_text: String,
+}
+
+impl TesterFileSystem {
+    pub fn new(path_to_lint: PathBuf, source_text: String) -> Self {
+        Self { path_to_lint, source_text }
+    }
+}
+
+impl RuntimeFileSystem for TesterFileSystem {
+    fn read_to_string(&self, path: &Path) -> Result<String, std::io::Error> {
+        if path == self.path_to_lint {
+            return Ok(self.source_text.clone());
+        }
+
+        read_to_string(path)
+    }
+
+    fn write_file(&self, _path: &Path, _content: String) -> Result<(), std::io::Error> {
+        panic!("writing file should not be allowed in Tester");
+    }
+}
+
 pub struct Tester {
     rule_name: &'static str,
     plugin_name: &'static str,
@@ -484,9 +511,12 @@ impl Tester {
         let paths = vec![Arc::<OsStr>::from(path_to_lint.as_os_str())];
         let options =
             LintServiceOptions::new(cwd, paths).with_cross_module(self.plugins.has_import());
-        let mut lint_service = LintService::from_linter(linter, options);
+        let mut lint_service = LintService::new(linter, options).with_file_system(Box::new(
+            TesterFileSystem::new(path_to_lint, source_text.to_string()),
+        ));
+
         let (sender, _receiver) = mpsc::channel();
-        let result = lint_service.run_test_source(&allocator, source_text, false, &sender);
+        let result = lint_service.run_test_source(&allocator, false, &sender);
 
         if result.is_empty() {
             return TestResult::Passed;