Check the tool runtime's own code before it merges, every test on a bus of its own (hq ADR 0237)

A merge-check.sh, the repository's layer of the mesh's merge check (mesh/repo-check):
format, vet, and node-tools' suite under the race detector. The tests shared one bus and
had to run one package at a time; like the controller's (#97), each now starts a server
of its own at the release go.mod pins, held to the catalogue's bus image by a test. What
cannot run in the check — bundles that need @novox/mesh-sdk — is said as not tested.

node-tools/internal/meshtest/meshtest_test.go

@@ -0,0 +1,75 @@
+package meshtest
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"testing"
+)
+
+// **The bus the tests run is the bus the mesh runs** (novox/hq ADR 0227 rule 9, ADR 0237): the server linked
+// into the tests is held to the release the catalogue's bus image is — read from beside this checkout, as
+// the build seat clones it for a merge check — and, given the facts snapshot, to the release the mesh's bus
+// server says it runs. A bus upgrade moves the catalogue's pin; this then fails until go.mod's moves with it.
+func TestTheBusTheTestsRunIsTheBusTheMeshRuns(t *testing.T) {
+	beside := os.Getenv("MESH_CHECK_BESIDE")
+	if beside == "" {
+		beside = filepath.Join("..", "..", "..", "..")
+	}
+	dockerfile := filepath.Join(beside, "mesh-catalog", "modules", "nats", "Dockerfile")
+	raw, err := os.ReadFile(dockerfile)
+	switch {
+	case err == nil:
+		pinned := regexp.MustCompile(`upstream: nats ([0-9.]+)-alpine`).FindSubmatch(raw)
+		if pinned == nil {
+			t.Fatalf("%s says no release its digest is", dockerfile)
+		}
+		if string(pinned[1]) != Version {
+			t.Errorf("the tests run bus %s and the catalogue's bus image is %s: move go.mod's nats-server pin with the image",
+				Version, pinned[1])
+		}
+	case os.IsNotExist(err):
+		t.Logf("the catalogue is not beside this checkout, so its bus image is not compared")
+	default:
+		t.Fatal(err)
+	}
+	path := os.Getenv("MESH_FACTS")
+	if path == "" {
+		t.Logf("no MESH_FACTS: the bus the mesh runs is compared in a merge check, which has it")
+		return
+	}
+	body, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatal(err)
+	}
+	var f struct {
+		Taken    string `json:"taken"`
+		Versions struct {
+			Bus string `json:"bus"`
+		} `json:"versions"`
+	}
+	if err := json.Unmarshal(body, &f); err != nil {
+		t.Fatal(err)
+	}
+	if f.Versions.Bus != "" && strings.TrimPrefix(f.Versions.Bus, "v") != Version {
+		t.Errorf("the tests run bus %s and the mesh's bus runs %s (facts of %s)", Version, f.Versions.Bus, f.Taken)
+	}
+}
+
+// Each test is given a bus of its own, and the same one at every ask.
+func TestEachTestHasABusOfItsOwn(t *testing.T) {
+	var first string
+	t.Run("one", func(t *testing.T) {
+		first = URL(t)
+		if URL(t) != first {
+			t.Fatal("two buses for one test")
+		}
+	})
+	t.Run("two", func(t *testing.T) {
+		if URL(t) == first {
+			t.Fatal("two tests were given one bus")
+		}
+	})
+}