log: make it easier to add parameters to JSON logging

fs/log_test.go

@@ -1,6 +1,28 @@
 package fs
 
-import "github.com/spf13/pflag"
+import (
+	"fmt"
+	"testing"
+
+	"github.com/spf13/pflag"
+	"github.com/stretchr/testify/assert"
+)
 
 // Check it satisfies the interface
 var _ pflag.Value = (*LogLevel)(nil)
+var _ fmt.Stringer = LogValueItem{}
+
+type withString struct{}
+
+func (withString) String() string {
+	return "hello"
+}
+
+func TestLogValue(t *testing.T) {
+	x := LogValue("x", 1)
+	assert.Equal(t, "1", x.String())
+	x = LogValue("x", withString{})
+	assert.Equal(t, "hello", x.String())
+	x = LogValueHide("x", withString{})
+	assert.Equal(t, "", x.String())
+}