Run Golang tests, capturing the Uber zap() output to a memory buffer

testWithCapture.go

testwithcapture.go

// testWithCapturedZapOutput runs a test and captures zap.L() outputs
func testWithCapturedZapOutput(testToRun func(t *testing.T), t *testing.T) string {
	var buffer bytes.Buffer

	origLogger := zap.L()
	defer func() {
		zap.L().Sync()
		zap.ReplaceGlobals(origLogger)
	}()

	encoder := zapcore.NewConsoleEncoder(zap.NewDevelopmentEncoderConfig())
	writer := bufio.NewWriter(&buffer)

	logger := zap.New(
		zapcore.NewCore(encoder, zapcore.AddSync(writer), zapcore.DebugLevel))
	zap.ReplaceGlobals(logger)

	testToRun(t)
	writer.Flush()

	return buffer.String()
}

// add this to top of test function to get zap logging. 
// then run test with -v (verbose) option 
oldlogger := zap.L()
// reset logger after this test completes
defer func() {
	zap.L().Sync()
	zap.ReplaceGlobals(oldlogger)
}()

// create a default logger that writes to stdout, stderr and enables DebugLevel
logger, _ := zap.NewDevelopment() 
zap.ReplaceGlobals(logger)