test(chrome): one launch preamble, and parity now pins ground truth

48 of 51 call sites shared one eight-line block that opened a fixture server,
launched chrome and checked the error. The three left are the launch tests
themselves, where what the helper hardcodes is the subject.

The audit called four tests superseded by fact_parity_test.go. They were not:
parity asserts the two producers agree and that each fact appears both ways,
never that either reading is right, so deleting them would have removed the only
thing anchoring the pair to reality. The values they pinned are now asserted
inside parity against both producers, and the shadow fixture has ground truth
where it had none.

internal/driver/chrome/selector_parity_test.go

@@ -5,13 +5,10 @@ package chrome
 import (
 	"context"
 	"encoding/json"
-	"net/http"
-	"net/http/httptest"
 	"path/filepath"
 	"slices"
 	"strings"
 	"testing"
-	"time"
 
 	"github.com/chromedp/chromedp"
 
@@ -31,16 +28,7 @@ import (
 // This test starts from one real page in a real browser and asks both matchers
 // the same questions.
 func TestSelectors_ResolveTheSameElementsAsTheWebRuntime(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
@@ -381,16 +369,7 @@ func TestSelectors_ResolveTheSameElementsAsTheWebRuntime(t *testing.T) {
 // turned the whole selector into a parse error: querySelectorAll throws, and
 // what a spec sees is an exception out of the extractor rather than an element.
 func TestSelectors_SecureCombinesWithAnotherKey(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)
@@ -426,16 +405,7 @@ func TestSelectors_SecureCombinesWithAnotherKey(t *testing.T) {
 // has an opinion about (everything is enabled, almost nothing is checked)
 // answers with most of the document and a want list nobody can check by reading.
 func TestSelectors_BooleanStatesNameWhatBothProducersReport(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)
@@ -619,16 +589,7 @@ func TestSelectors_BooleanStatesNameWhatBothProducersReport(t *testing.T) {
 // '[id="state_month"]select' and querySelectorAll threw a SyntaxError. Which of
 // the two a spec got depended on the order its author wrote the keys in.
 func TestSelectors_TagCombinesWithAnotherKey(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)
@@ -661,16 +622,7 @@ func TestSelectors_TagCombinesWithAnotherKey(t *testing.T) {
 // ancestors up to the document root read as matches too, and the deepest one is
 // the element the author meant.
 func TestSelectors_TextNamesTheInnermostMatchInEveryResolver(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)
@@ -825,16 +777,7 @@ func TestSelectors_TextNamesTheInnermostMatchInEveryResolver(t *testing.T) {
 // "January" is not clickable: resolving text to its own innermost match before
 // the other keys narrow anything answers with nothing in both.
 func TestSelectors_TextCombinesWithAnotherKey(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)
@@ -971,16 +914,7 @@ func xpathIDsOverCDP(
 // step, resolving the target in the dump and tapping it over CDP, so a selector
 // the two read differently taps one element and reads the text of another.
 func TestSelectors_DataTestIDNamesTheSameElementInTheDumpAndOverCDP(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)
@@ -1026,16 +960,7 @@ func TestSelectors_DataTestIDNamesTheSameElementInTheDumpAndOverCDP(t *testing.T
 // already does. placeholder keeps its CSS: it is the attribute the markup
 // writes, which is what all three resolvers read it as.
 func TestSelectors_HintSelectorsResolveOverCDPToWhatBothMatchersName(t *testing.T) {
-	server := httptest.NewServer(http.FileServer(http.Dir("testdata")))
-	defer server.Close()
-
-	d := New()
-	defer d.Terminate(context.Background())
-	ctx, cancel := context.WithTimeout(context.Background(), 60*time.Second)
-	defer cancel()
-	if err := d.Launch(ctx, server.URL+"/selector-parity.html", false, nil); err != nil {
-		t.Fatalf("Launch: %v", err)
-	}
+	d, ctx := launchChrome(t, testdataServer(t).URL+"/selector-parity.html")
 	dump, err := d.Hierarchy(ctx)
 	if err != nil {
 		t.Fatalf("Hierarchy: %v", err)