Check log message for a string

gistfile1.txt

/* 
Ex. output
{"File":"xyx.xyz/../../../some.go","Function":"xyz.xyz/../../package.FunctionName,"Line":36,"level":"error","msg":"Unsupported base image","time":"2024-06-06T12:29:40.032+0530"}
*/
func checkInvalidImage(c *qt.C, imageName, expected string) {
	// Capture stderr via a pipe
	stdErrC := make(chan *bytes.Buffer)
	pR, pW, err := os.Pipe()
	c.Assert(err, qt.IsNil)
	go func() {
		var buf bytes.Buffer
		io.Copy(&buf, pR)
		pR.Close()
		stdErrC <- &buf
	}()

	// Save and redirect stderr
	var savedStderr = os.Stderr
	defer func() {
		os.Stderr = savedStderr
		log.SetOutput(log.StderrSink)
	}()
	os.Stderr = pW
	log.SetOutput(log.StderrSink)
	var result = GetKanisterImage(imageName)
	// Close pipe writer and capture stderr output
	pW.Close()
	stderr := <-stdErrC
	c.Assert(result, qt.Equals, expected)

	re := regexp.MustCompile(`"msg"\s*:\s*"([^"]+)"`)
	matches := re.FindAllStringSubmatch(stderr.String(), -1)
	c.Assert(len(matches), qt.Equals, 1)
	c.Assert(matches[0][1], qt.Equals, unsupportedErrorMsg)
}