diff --git a/config/file/format_test.go b/config/file/format_test.go
new file mode 100644
index 000000000..509a98379
--- /dev/null
+++ b/config/file/format_test.go
@@ -0,0 +1,41 @@
+package file
+
+import "testing"
+
+func TestFormat(t *testing.T) {
+	tests := []struct {
+		input  string
+		expect string
+	}{
+		{
+			input:  "",
+			expect: "",
+		},
+		{
+			input:  " ",
+			expect: "",
+		},
+		{
+			input:  ".",
+			expect: "",
+		},
+		{
+			input:  "a.",
+			expect: "",
+		},
+		{
+			input:  ".b",
+			expect: "b",
+		},
+		{
+			input:  "a.b",
+			expect: "b",
+		},
+	}
+	for _, v := range tests {
+		content := format(v.input)
+		if got, want := content, v.expect; got != want {
+			t.Errorf("expect %v,got %v", want, got)
+		}
+	}
+}