1 files changed, 44 insertions, 0 deletions
diff --git a/cmd/internal/hexai-action/main_test.go b/cmd/internal/hexai-action/main_test.go
new file mode 100644
index 0000000..9603826
--- /dev/null
+++ b/cmd/internal/hexai-action/main_test.go
@@ -0,0 +1,44 @@
+package main
+
+import (
+    "io"
+    "os"
+    "path/filepath"
+    "testing"
+)
+
+// TestOpenIO_InOutFiles verifies that openIO opens the specified files
+// and that writing via the returned writer persists to disk.
+func TestOpenIO_InOutFiles(t *testing.T) {
+    dir := t.TempDir()
+    inPath := filepath.Join(dir, "in.txt")
+    outPath := filepath.Join(dir, "out.txt")
+
+    // Prepare input file
+    want := "hello world"
+    if err := os.WriteFile(inPath, []byte(want), 0o600); err != nil {
+        t.Fatalf("write infile: %v", err)
+    }
+
+    in, out, cin, cout, err := openIO(inPath, outPath)
+    if err != nil {
+        t.Fatalf("openIO: %v", err)
+    }
+    defer cin()
+    defer cout()
+
+    // Copy through to simulate main's behavior
+    if _, err := io.Copy(out.(io.Writer), in); err != nil {
+        t.Fatalf("copy: %v", err)
+    }
+
+    // Verify outfile content
+    got, err := os.ReadFile(outPath)
+    if err != nil {
+        t.Fatalf("read outfile: %v", err)
+    }
+    if string(got) != want {
+        t.Fatalf("mismatch: got %q want %q", string(got), want)
+    }
+}
+