flag/stat: fix omitted stat in error log level

Create unit & e2e tests
Fixes peak#359

Co-Authored-By: Muhammed Can Küçükaslan <[email protected]>

log/log_test.go

@@ -0,0 +1,59 @@
+package log
+
+import (
+	"bytes"
+	"fmt"
+	"github.com/peak/s5cmd/log/stat"
+	"io"
+	"os"
+	"strings"
+	"testing"
+)
+
+func TestStat(t *testing.T) {
+	levels := []string{
+		"trace",
+		"debug",
+		"info",
+		"error",
+	}
+	for _, l := range levels {
+		testStatHelper(l, t)
+	}
+	// testStatHelper method closes and remakes the outputCh
+	// but this creates a useless channel at the end too
+	// so we need to close it at the end.
+	Close()
+}
+
+func testStatHelper(level string, t *testing.T) {
+	old := os.Stdout // keep backup of the real stdout
+	r, w, _ := os.Pipe()
+	os.Stdout = w
+
+	Init(level, true)
+	op := "op"
+
+	var s, e int64 = 1, 0
+	Stat(stat.Stats{{op, s, e}})
+
+	// Close closes the output channel so that the current test level can have its output.
+	Close()
+	// To be able to test the remaining tests, we should create new channel for them
+	outputCh = make(chan output, 10000)
+	outC := make(chan string)
+	// copy the output in a separate goroutine so printing can't block indefinitely
+	go func() {
+		var buf bytes.Buffer
+		io.Copy(&buf, r)
+		outC <- buf.String()
+	}()
+	// back to normal state
+	w.Close()
+	os.Stdout = old // restoring the real stdout
+	out := <-outC
+	out = strings.TrimSpace(out)
+	if out != fmt.Sprintf("{\"operation\":\"%s\",\"success\":%v,\"error\":%v}", op, s, e) {
+		t.Errorf("Stat does not print in %v level!\n$%v$", level, out)
+	}
+}