feat(runner): skip a step whose tree changed between two reads

internal/runner/composition_reread_test.go

@@ -0,0 +1,156 @@
+package runner
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+	"sync/atomic"
+	"testing"
+	"time"
+
+	"github.com/priyanshujain/sanderling/internal/driver"
+	mockdriver "github.com/priyanshujain/sanderling/internal/driver/mock"
+)
+
+// homeWithRows is one settled route whose list holds rows. A row arriving
+// between two reads is what a Compose lazy list mounting over several frames
+// looks like from the runner's side.
+func homeWithRows(rows int) string {
+	var children strings.Builder
+	for row := range rows {
+		fmt.Fprintf(&children,
+			`,{"attributes":{"resource-id":"TxnRow%d","class":"android.view.View"},"children":[]}`, row)
+	}
+	return fmt.Sprintf(
+		`{"attributes":{"resource-id":"HomeScreen","class":"android.view.View"},"children":[
+		  {"attributes":{"resource-id":"TxnList","class":"android.view.View"},"children":[]}%s
+		]}`, children.String())
+}
+
+// composesLateDriver answers the paired Snapshot with the frame the step
+// records and the hierarchy read that follows with a tree that has grown a row,
+// for the first composingReads reads of the run. After that both reads describe
+// the same screen.
+type composesLateDriver struct {
+	*mockdriver.Driver
+	composingReads int64
+	reads          atomic.Int64
+}
+
+func (d *composesLateDriver) Snapshot(context.Context) (string, driver.Image, error) {
+	return homeWithRows(1), driver.Image{PNG: []byte("png"), Width: 1, Height: 1}, nil
+}
+
+func (d *composesLateDriver) Hierarchy(context.Context) (string, error) {
+	if d.reads.Add(1) <= d.composingReads {
+		return homeWithRows(2), nil
+	}
+	return homeWithRows(1), nil
+}
+
+// A route can settle before its content composes, so a tree read the moment the
+// route arrives can describe a screen that is still filling in. Verifying that
+// step compares a half-composed frame against a settled one and convicts an app
+// that did nothing wrong. Two reads a read apart see it happening, and the step
+// they disagree on is one the verifier must never be handed.
+//
+// The always-false property is the witness: it fires on the first step the
+// verifier evaluates, so the step index of its violation says exactly which
+// step reached the verifier.
+func TestRunner_AStepWhoseTreeChangedBetweenReadsIsNotVerified(t *testing.T) {
+	run := func(t *testing.T, composingReads int64) (Summary, string) {
+		t.Helper()
+		state := newHarnessWithSpec(t, violationSpec)
+		device := &composesLateDriver{Driver: state.mock, composingReads: composingReads}
+
+		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		defer cancel()
+		summary, err := Run(ctx, Options{
+			Duration:    time.Hour,
+			IdleTimeout: 20 * time.Millisecond,
+			MaxSteps:    3,
+			Driver:      device,
+			Verifier:    state.verifier,
+			TraceWriter: state.writer,
+		})
+		if err != nil {
+			t.Fatalf("Run: %v", err)
+		}
+		if summary.Steps != 3 {
+			t.Fatalf("steps = %d, want 3", summary.Steps)
+		}
+		return summary, state.writer.Directory()
+	}
+
+	t.Run("the step it changed on is skipped, the next one is judged", func(t *testing.T) {
+		summary, directory := run(t, 1)
+		if len(summary.Violations) != 1 {
+			t.Fatalf("violations = %v, want exactly one", summary.Violations)
+		}
+		violation := summary.Violations[0]
+		if violation.Properties[0] != "balanceNonNegative" {
+			t.Fatalf("violated %v, want balanceNonNegative", violation.Properties)
+		}
+		if violation.StepIndex != 2 {
+			t.Errorf("the property first judged step %d, want 2; the verifier was handed "+
+				"a screen that grew a row while the runner was reading it",
+				violation.StepIndex)
+		}
+		if summary.SkippedVerification != 1 {
+			t.Errorf("the run reports %d step(s) judged by nothing, want 1",
+				summary.SkippedVerification)
+		}
+		// Skipped is not lost: the step is still recorded, screenshot and all,
+		// so the run can be replayed over the frame nothing judged.
+		steps := traceSteps(t, directory)
+		if len(steps) != 3 {
+			t.Fatalf("trace holds %d step(s), want 3", len(steps))
+		}
+		if len(steps[0].Violations) != 0 {
+			t.Errorf("step 1 recorded violations %v; it was never verified", steps[0].Violations)
+		}
+		screenshot := filepath.Join(directory, "screenshots", "step-00001.png")
+		if _, err := os.Stat(screenshot); err != nil {
+			t.Errorf("expected the skipped step's screenshot at %s: %v", screenshot, err)
+		}
+	})
+
+	// The control. Two reads that agree must verify as they always did,
+	// otherwise the case above is just a runner that verifies nothing.
+	t.Run("two reads that agree verify the step", func(t *testing.T) {
+		summary, _ := run(t, 0)
+		if len(summary.Violations) != 1 {
+			t.Fatalf("violations = %v, want exactly one", summary.Violations)
+		}
+		if got := summary.Violations[0].StepIndex; got != 1 {
+			t.Errorf("the property first judged step %d, want 1; a settled screen must be "+
+				"verified on the step it was read", got)
+		}
+	})
+}
+
+type traceLine struct {
+	Step       int      `json:"step"`
+	Violations []string `json:"violations"`
+}
+
+func traceSteps(t *testing.T, directory string) []traceLine {
+	t.Helper()
+	body, err := os.ReadFile(filepath.Join(directory, "trace.jsonl"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	var steps []traceLine
+	for _, raw := range bytes.Split(bytes.TrimSpace(body), []byte("\n")) {
+		var line traceLine
+		if err := json.Unmarshal(raw, &line); err != nil {
+			t.Fatalf("decode trace line: %v", err)
+		}
+		steps = append(steps, line)
+	}
+	return steps
+}