refactor: we don't wanna export pkg/oonimkall/tasks (#216)

* doc: merge the engine and the cli readmes

Part of https://github.com/ooni/probe/issues/1335

* refactor: we don't wanna export pkg/oonimkall/tasks

See https://github.com/ooni/probe/issues/1335

pkg/oonimkall/internal/tasks/eventemitter_test.go

@@ -0,0 +1,67 @@
+package tasks_test
+
+import (
+	"testing"
+
+	"github.com/ooni/probe-cli/v3/pkg/oonimkall/internal/tasks"
+)
+
+func TestDisabledEvents(t *testing.T) {
+	out := make(chan *tasks.Event)
+	emitter := tasks.NewEventEmitter([]string{"log"}, out)
+	go func() {
+		emitter.Emit("log", tasks.EventLog{Message: "foo"})
+		close(out)
+	}()
+	var count int64
+	for ev := range out {
+		if ev.Key == "log" {
+			count++
+		}
+	}
+	if count > 0 {
+		t.Fatal("cannot disable events")
+	}
+}
+
+func TestEmitFailureStartup(t *testing.T) {
+	out := make(chan *tasks.Event)
+	emitter := tasks.NewEventEmitter([]string{}, out)
+	go func() {
+		emitter.EmitFailureStartup("mocked error")
+		close(out)
+	}()
+	var found bool
+	for ev := range out {
+		if ev.Key == "failure.startup" {
+			evv := ev.Value.(tasks.EventFailure) // panic if not castable
+			if evv.Failure == "mocked error" {
+				found = true
+			}
+		}
+	}
+	if !found {
+		t.Fatal("did not see expected event")
+	}
+}
+
+func TestEmitStatusProgress(t *testing.T) {
+	out := make(chan *tasks.Event)
+	emitter := tasks.NewEventEmitter([]string{}, out)
+	go func() {
+		emitter.EmitStatusProgress(0.7, "foo")
+		close(out)
+	}()
+	var found bool
+	for ev := range out {
+		if ev.Key == "status.progress" {
+			evv := ev.Value.(tasks.EventStatusProgress) // panic if not castable
+			if evv.Message == "foo" && evv.Percentage == 0.7 {
+				found = true
+			}
+		}
+	}
+	if !found {
+		t.Fatal("did not see expected event")
+	}
+}