Mock a go-logr and verify the message it logs?


Im using the following go-logr/logr library.
I have a test which needs to pass the logger as parameter and check that it was able to log the data that was sent.

I need to test the function GetConfig:

config, err := GetConfig(FilePath, "ns", logger, "test" )

At the end I need to print some message from the logger in the test


My question is how should mock it?

I’ve tried with the following but without success

func NewTestLogger() logr.Logger {
    l := &testlogger{
        Formatter: funcr.NewFormatter(funcr.Options{}),
    return logr.New(l)

var _ = Describe(“test” action, func() {
    It("action configuration with  logger", func() {

        //var t *testing.T
        tl := NewTestLogger()
        config, err := GetConfig(kcfgFilePath, "ns", tl, "test")

But Im not able to print the value from the logger, how can I do it right?

Something like 

assert.Contains(t, tl.sink.Output, "test")

Should I use the testing package?

This is a working version without the assertion.
Not sure what I miss there as I want to assert the data that are coming from the output of the GetConfig ‘tl` and get the key and value

This is close to the code I’ve in prod, how can I make work?

My Question is how should I assert the following

assert.Contains(t, tl.GetSink().WithName("Output"), "test") 
assert.Contains(t, tl.GetSink().WithName("Output"), "message") 
assert.Contains(t, tl.GetSink().WithName("Output"), "print something") 

I was able to get the data like following, but not sure how to assert the values


The logr.New function accepts any implementation of the LogSink interface – This means you should just implement one that saves the calls onto a slice in-memory instead of printing, and then you can expect that the slice has your log output.

package main

import (
    // ... some extra imports

type TestLogger struct {
    Output map[string]map[int][]interface{}
    r RuntimeInfo
func (t *TestLogger) doLog(level int, msg string, keysAndValues ...interface{}) {
    m := make(map[int][]interface{}, len(keysAndValues))
    m[level] = keysAndValues
    t.output[msg] = m
func (t *TestLogger) Init(info RuntimeInfo) { t.r = info}
func (t *TestLogger) Enabled(level int) bool {return true}
func (t *TestLogger) Info(level int, msg string, keysAndValues ...interface{}) { t.doLog(level, msg, keysAndValues...) }
func (t *TestLogger) Error(err error, msg string, keysAndValues ...interface{}) { t.doLog(level, msg, append(keysAndValues, err)...) }
func (t *TestLogger) WithValues(keysAndValues ...interface{}) LogSink { return t}
func (t *TestLogger) WithName(name string) LogSink { return t }

func TestLoggerHasOutput(t *testing.T) {

        l := &TestLogger{make(map[string]map[int][]interface[]), RuntimeInfo{1}}
        tl := logr.New(l)
        config, err := GetConfig(kcfgFilePath, "ns", tl, "test")
        assert.Contains(t, l.Output, "ns") // you can also test the contents of the output as well

Answered By – Chaos Monkey

Answer Checked By – Mildred Charles (GoLangFix Admin)

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