feat: tutorial on how to write the torsf experiment (#390)

Original tracking issue for Sprint 41: https://github.com/ooni/probe/issues/1507

Follow-up work in Sprint 42 tracked by: https://github.com/ooni/probe/issues/1689

internal/engine/mockable/mockable.go

@@ -0,0 +1,144 @@
+// Package mockable contains mockable objects
+package mockable
+
+import (
+	"context"
+	"net/http"
+	"net/url"
+
+	"github.com/ooni/probe-cli/v3/internal/engine/model"
+	"github.com/ooni/probe-cli/v3/internal/engine/probeservices"
+	"github.com/ooni/probe-cli/v3/internal/kvstore"
+)
+
+// Session allows to mock sessions.
+type Session struct {
+	MockableTestHelpers              map[string][]model.Service
+	MockableHTTPClient               *http.Client
+	MockableLogger                   model.Logger
+	MockableMaybeResolverIP          string
+	MockableProbeASNString           string
+	MockableProbeCC                  string
+	MockableProbeIP                  string
+	MockableProbeNetworkName         string
+	MockableProxyURL                 *url.URL
+	MockableFetchPsiphonConfigResult []byte
+	MockableFetchPsiphonConfigErr    error
+	MockableFetchTorTargetsResult    map[string]model.TorTarget
+	MockableFetchTorTargetsErr       error
+	MockableFetchURLListResult       []model.URLInfo
+	MockableFetchURLListErr          error
+	MockableResolverIP               string
+	MockableSoftwareName             string
+	MockableSoftwareVersion          string
+	MockableTempDir                  string
+	MockableTorArgs                  []string
+	MockableTorBinary                string
+	MockableUserAgent                string
+}
+
+// GetTestHelpersByName implements ExperimentSession.GetTestHelpersByName
+func (sess *Session) GetTestHelpersByName(name string) ([]model.Service, bool) {
+	services, okay := sess.MockableTestHelpers[name]
+	return services, okay
+}
+
+// DefaultHTTPClient implements ExperimentSession.DefaultHTTPClient
+func (sess *Session) DefaultHTTPClient() *http.Client {
+	return sess.MockableHTTPClient
+}
+
+// FetchPsiphonConfig implements ExperimentSession.FetchPsiphonConfig
+func (sess *Session) FetchPsiphonConfig(ctx context.Context) ([]byte, error) {
+	return sess.MockableFetchPsiphonConfigResult, sess.MockableFetchPsiphonConfigErr
+}
+
+// FetchTorTargets implements ExperimentSession.TorTargets
+func (sess *Session) FetchTorTargets(
+	ctx context.Context, cc string) (map[string]model.TorTarget, error) {
+	return sess.MockableFetchTorTargetsResult, sess.MockableFetchTorTargetsErr
+}
+
+// FetchURLList implements ExperimentSession.FetchURLList.
+func (sess *Session) FetchURLList(
+	ctx context.Context, config model.URLListConfig) ([]model.URLInfo, error) {
+	return sess.MockableFetchURLListResult, sess.MockableFetchURLListErr
+}
+
+// KeyValueStore returns the configured key-value store.
+func (sess *Session) KeyValueStore() model.KeyValueStore {
+	return &kvstore.Memory{}
+}
+
+// Logger implements ExperimentSession.Logger
+func (sess *Session) Logger() model.Logger {
+	return sess.MockableLogger
+}
+
+// MaybeResolverIP implements ExperimentSession.MaybeResolverIP.
+func (sess *Session) MaybeResolverIP() string {
+	return sess.MockableMaybeResolverIP
+}
+
+// ProbeASNString implements ExperimentSession.ProbeASNString
+func (sess *Session) ProbeASNString() string {
+	return sess.MockableProbeASNString
+}
+
+// ProbeCC implements ExperimentSession.ProbeCC
+func (sess *Session) ProbeCC() string {
+	return sess.MockableProbeCC
+}
+
+// ProbeIP implements ExperimentSession.ProbeIP
+func (sess *Session) ProbeIP() string {
+	return sess.MockableProbeIP
+}
+
+// ProbeNetworkName implements ExperimentSession.ProbeNetworkName
+func (sess *Session) ProbeNetworkName() string {
+	return sess.MockableProbeNetworkName
+}
+
+// ProxyURL implements ExperimentSession.ProxyURL
+func (sess *Session) ProxyURL() *url.URL {
+	return sess.MockableProxyURL
+}
+
+// ResolverIP implements ExperimentSession.ResolverIP
+func (sess *Session) ResolverIP() string {
+	return sess.MockableResolverIP
+}
+
+// SoftwareName implements ExperimentSession.SoftwareName
+func (sess *Session) SoftwareName() string {
+	return sess.MockableSoftwareName
+}
+
+// SoftwareVersion implements ExperimentSession.SoftwareVersion
+func (sess *Session) SoftwareVersion() string {
+	return sess.MockableSoftwareVersion
+}
+
+// TempDir implements ExperimentSession.TempDir
+func (sess *Session) TempDir() string {
+	return sess.MockableTempDir
+}
+
+// TorArgs implements ExperimentSession.TorArgs.
+func (sess *Session) TorArgs() []string {
+	return sess.MockableTorArgs
+}
+
+// TorBinary implements ExperimentSession.TorBinary.
+func (sess *Session) TorBinary() string {
+	return sess.MockableTorBinary
+}
+
+// UserAgent implements ExperimentSession.UserAgent
+func (sess *Session) UserAgent() string {
+	return sess.MockableUserAgent
+}
+
+var _ model.ExperimentSession = &Session{}
+var _ probeservices.Session = &Session{}