diff --git a/README.md b/README.md
index 0584d9a..94ed2cb 100644
--- a/README.md
+++ b/README.md
@@ -44,6 +44,8 @@
     <a href="https://github.com/speakeasy-api/openapi/actions/workflows/ci.yaml"><img alt="Security" src="https://img.shields.io/badge/security-scanned-green.svg?style=for-the-badge&logo=security"></a>
     <!-- CI Badge -->
     <a href="https://github.com/speakeasy-api/openapi/actions/workflows/ci.yaml"><img alt="GitHub Action: CI" src="https://img.shields.io/github/actions/workflow/status/speakeasy-api/openapi/ci.yaml?style=for-the-badge"></a>
+    <!-- Coverage Badge -->
+    <a href="https://app.codecov.io/gh/speakeasy-api/openapi"><img alt="Code coverage" src="https://img.shields.io/codecov/c/github/speakeasy-api/openapi/main?style=for-the-badge"></a>
     <!-- Line Break --><br/>
     <!-- Go Version Badge -->
     <a href="https://golang.org/"><img alt="Go Version" src="https://img.shields.io/badge/go-1.24.3+-00ADD8.svg?style=for-the-badge&logo=go"></a>
diff --git a/overlay/parse_test.go b/overlay/parse_test.go
index fe0c2ad..79ba921 100644
--- a/overlay/parse_test.go
+++ b/overlay/parse_test.go
@@ -2,6 +2,7 @@ package overlay_test
 
 import (
 	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/speakeasy-api/openapi/overlay"
@@ -12,12 +13,17 @@ import (
 func TestParse(t *testing.T) {
 	t.Parallel()
 
-	err := overlay.Format("testdata/overlay.yaml")
+	fixture, err := os.ReadFile("testdata/overlay.yaml")
+	require.NoError(t, err, "overlay fixture should load")
+	path := filepath.Join(t.TempDir(), "overlay.yaml")
+	require.NoError(t, os.WriteFile(path, fixture, 0o600), "private overlay fixture should be created")
+
+	err = overlay.Format(path)
 	require.NoError(t, err)
-	o, err := overlay.Parse("testdata/overlay.yaml")
+	o, err := overlay.Parse(path)
 	require.NoError(t, err)
 	assert.NotNil(t, o)
-	expect, err := os.ReadFile("testdata/overlay.yaml")
+	expect, err := os.ReadFile(path)
 	require.NoError(t, err)
 
 	actual, err := o.ToString()