tests: add util tests

internal/utils/fs_utils_test.go

@@ -0,0 +1,31 @@
+package utils
+
+import (
+	"os"
+	"testing"
+
+	"gotest.tools/v3/assert"
+)
+
+func TestReadFile(t *testing.T) {
+	// Setup
+	file, err := os.Create("/tmp/tinyauth_test_file")
+	assert.NilError(t, err)
+
+	_, err = file.WriteString("file content\n")
+	assert.NilError(t, err)
+
+	err = file.Close()
+	assert.NilError(t, err)
+	defer os.Remove("/tmp/tinyauth_test_file")
+
+	// Normal case
+	content, err := ReadFile("/tmp/tinyauth_test_file")
+	assert.NilError(t, err)
+	assert.Equal(t, "file content\n", content)
+
+	// Non-existing file
+	content, err = ReadFile("/tmp/non_existing_file")
+	assert.ErrorContains(t, err, "no such file or directory")
+	assert.Equal(t, "", content)
+}