test: cover web-runtime seeded PRNG, weighted pick, and seed define wiring

internal/bundler/web_bundle_test.go

@@ -122,6 +122,38 @@ func TestBundleWeb_IsDeterministic(t *testing.T) {
 	}
 }
 
+// TestBundleWeb_InjectsSeedDefine asserts that a SANDERLING_SEED define is
+// inlined into the bundle so --seed reaches the web runtime PRNG. esbuild
+// replaces process.env.SANDERLING_SEED with the quoted literal at build time.
+func TestBundleWeb_InjectsSeedDefine(t *testing.T) {
+	directory := t.TempDir()
+	runtimePath := filepath.Join(directory, "web-runtime.ts")
+	specPath := filepath.Join(directory, "spec.ts")
+	runtime := fakeRuntime + "\n(globalThis as Record<string, unknown>).__seed = process.env.SANDERLING_SEED;\n"
+	if err := os.WriteFile(runtimePath, []byte(runtime), 0o644); err != nil {
+		t.Fatal(err)
+	}
+	if err := os.WriteFile(specPath, []byte(fakeSpec), 0o644); err != nil {
+		t.Fatal(err)
+	}
+
+	result, err := BundleWeb(WebOptions{
+		EntryFile:      specPath,
+		WebRuntimeFile: runtimePath,
+		Defines:        map[string]string{"SANDERLING_SEED": "8675309"},
+	})
+	if err != nil {
+		t.Fatalf("BundleWeb: %v", err)
+	}
+	source := string(result.JavaScript)
+	if !strings.Contains(source, "8675309") {
+		t.Errorf("seed literal not inlined into bundle\nsource head:\n%s", head(source, 500))
+	}
+	if strings.Contains(source, "process.env.SANDERLING_SEED") {
+		t.Errorf("define left unsubstituted in bundle")
+	}
+}
+
 func head(text string, max int) string {
 	if len(text) <= max {
 		return text

internal/testrun/testrun_test.go

@@ -3,9 +3,31 @@ package testrun
 import (
 	"os"
 	"path/filepath"
+	"strconv"
 	"testing"
 )
 
+func TestResolveSeed_UsesConfiguredWhenNonZero(t *testing.T) {
+	if got := resolveSeed(42); got != 42 {
+		t.Fatalf("got %d, want 42", got)
+	}
+}
+
+func TestResolveSeed_DerivesWhenZero(t *testing.T) {
+	if got := resolveSeed(0); got == 0 {
+		t.Fatal("expected a non-zero time-derived seed")
+	}
+}
+
+// TestSeedDefineFormatsAsDecimal guards the contract that Execute uses to put
+// the seed into the web bundle: strconv.FormatInt base 10, which web-runtime
+// folds to a 32-bit PRNG seed.
+func TestSeedDefineFormatsAsDecimal(t *testing.T) {
+	if got := strconv.FormatInt(resolveSeed(8675309), 10); got != "8675309" {
+		t.Fatalf("got %q, want 8675309", got)
+	}
+}
+
 func TestResolveSpecAPIPath_FindsUpwardSibling(t *testing.T) {
 	root := t.TempDir()
 	apiPath := filepath.Join(root, "pkg", "spec", "src", "index.ts")