feat(miniooni): optionally log using emojis (#932)

As silly as it seems, emojis help _a lot_ when eyeballing logs
to quickly identify unexpected lines.

I'm doing this work as part of https://github.com/ooni/probe/issues/2257

internal/logx/logx_test.go

@@ -0,0 +1,109 @@
+package logx
+
+import (
+	"fmt"
+	"os"
+	"testing"
+	"time"
+
+	"github.com/apex/log"
+	"github.com/google/go-cmp/cmp"
+	"github.com/ooni/probe-cli/v3/internal/model/mocks"
+	"github.com/ooni/probe-cli/v3/internal/testingx"
+)
+
+func TestNewHandlerWithDefaultSettings(t *testing.T) {
+	lh := NewHandlerWithDefaultSettings()
+	if lh.Emoji {
+		t.Fatal("expected false")
+	}
+	// Note: Go does not allow us to check whether lh.Now == time.Now
+	if lh.StartTime.IsZero() {
+		t.Fatal("expected non-zero time")
+	}
+	if lh.Writer != os.Stderr {
+		t.Fatal("expected stderr")
+	}
+}
+
+// creates a new handler with deterministic time to help with testing
+func newHandlerForTesting() *Handler {
+	lh := NewHandlerWithDefaultSettings()
+	dtime := testingx.NewTimeDeterministic(time.Now())
+	lh.Now = dtime.Now
+	lh.StartTime = dtime.Now()
+	return lh
+}
+
+func TestLogHandlerHandleLog(t *testing.T) {
+	type config struct {
+		// name of the test
+		Name string
+
+		// whether to use emojis
+		Emoji bool
+
+		// the verbosity level of the log entry
+		Level log.Level
+
+		// the string we expect for severity
+		ExpectSeverity string
+	}
+
+	configs := []config{{
+		Name:           "debug level without emoji",
+		Emoji:          false,
+		Level:          log.DebugLevel,
+		ExpectSeverity: "<debug>",
+	}, {
+		Name:           "info level without emoji",
+		Emoji:          false,
+		Level:          log.InfoLevel,
+		ExpectSeverity: "<info>",
+	}, {
+		Name:           "warn level without emoji",
+		Emoji:          false,
+		Level:          log.WarnLevel,
+		ExpectSeverity: "<warn>",
+	}, {
+		Name:           "debug level with emoji",
+		Emoji:          true,
+		Level:          log.DebugLevel,
+		ExpectSeverity: "🧐",
+	}, {
+		Name:           "info level with emoji",
+		Emoji:          true,
+		Level:          log.InfoLevel,
+		ExpectSeverity: "🗒️",
+	}, {
+		Name:           "warn level with emoji",
+		Emoji:          true,
+		Level:          log.WarnLevel,
+		ExpectSeverity: "🔥",
+	}}
+
+	for _, cnf := range configs {
+		t.Run(cnf.Name, func(t *testing.T) {
+			expected := fmt.Sprintf("[      1.000000] %s antani: map[error:EOF]\n", cnf.ExpectSeverity)
+			var got string
+			lh := newHandlerForTesting()
+			lh.Emoji = cnf.Emoji
+			lh.Writer = &mocks.Writer{
+				MockWrite: func(b []byte) (int, error) {
+					got = string(b)
+					return len(b), nil
+				},
+			}
+			lh.HandleLog(&log.Entry{
+				Fields: map[string]any{
+					"error": "EOF",
+				},
+				Level:   cnf.Level,
+				Message: "antani",
+			})
+			if diff := cmp.Diff(expected, got); diff != "" {
+				t.Fatal(diff)
+			}
+		})
+	}
+}