test: Use modern testing features instead of custom helpers

Many of our tests rely on helpers that predate features which are now
available in the standard library.

This patch replaces them with the standard equivalents:

- MustTempDir/RemoveIfOk -> t.ArtifactDir() or t.TempDir() (depending on
  whether it is useful to keep the data on request).
- GetFreePort + waitForServer -> opening the listeners before starting
  the servers. To support this, localrpc.Server gains a Serve method. We
  may re-introduce these in the future if more use cases appear.
- WaitFor and real-time timing checks -> testing/synctest.
- context.Background() -> t.Context().
- Benchmark b.N loops -> b.Loop().
- reflect.DeepEqual -> cmp.Diff, and proto.Equal for protobufs.

internal/testlib/testlib_test.go

@@ -1,107 +1,26 @@
 package testlib
 
 import (
-	"errors"
-	"io/fs"
 	"os"
 	"testing"
-	"time"
 )
 
-func TestBasic(t *testing.T) {
-	dir := MustTempDir(t)
-	if err := os.WriteFile(dir+"/file", nil, 0660); err != nil {
-		t.Fatalf("could not create file in %s: %v", dir, err)
-	}
-
-	wd, err := os.Getwd()
-	if err != nil {
-		t.Fatalf("could not get working directory: %v", err)
-	}
-	if wd != dir {
-		t.Errorf("MustTempDir did not change directory")
-		t.Errorf("  expected %q, got %q", dir, wd)
-	}
-
-	RemoveIfOk(t, dir)
-	if _, err := os.Stat(dir); !errors.Is(err, fs.ErrNotExist) {
-		t.Fatalf("%s existed, should have been deleted: %v", dir, err)
-	}
-}
-
-func TestRemoveCheck(t *testing.T) {
-	defer func() {
-		if r := recover(); r != nil {
-			t.Logf("recovered: %v", r)
-		} else {
-			t.Fatalf("check did not panic as expected")
-		}
-	}()
-
-	RemoveIfOk(t, "/tmp/something")
-}
-
-func TestLeaveDirOnError(t *testing.T) {
-	myt := &testing.T{}
-	dir := MustTempDir(myt)
-	myt.Errorf("something bad happened")
-
-	RemoveIfOk(myt, dir)
-	if _, err := os.Stat(dir); errors.Is(err, fs.ErrNotExist) {
-		t.Fatalf("%s was removed, should have been kept", dir)
-	}
-
-	// Remove the directory for real this time.
-	RemoveIfOk(t, dir)
-}
-
-func TestRewriteSafeguard(t *testing.T) {
-	myt := &testing.T{}
-	defer func() {
-		if r := recover(); r != nil {
-			t.Logf("recovered: %v", r)
-		} else {
-			t.Fatalf("check did not panic as expected")
-		}
-	}()
-
-	Rewrite(myt, "/something", "test")
-}
-
 func TestRewrite(t *testing.T) {
-	dir := MustTempDir(t)
-	defer RemoveIfOk(t, dir)
+	fname := t.TempDir() + "/file"
+	Rewrite(t, fname, "hola")
+	Rewrite(t, fname, "chau")
 
-	myt := &testing.T{}
-	Rewrite(myt, dir+"/file", "hola")
-	if myt.Failed() {
-		t.Errorf("basic rewrite failed")
+	data, err := os.ReadFile(fname)
+	if err != nil {
+		t.Fatalf("failed to read file: %v", err)
 	}
-}
-
-func TestGetFreePort(t *testing.T) {
-	p := GetFreePort()
-	if p == "" {
-		t.Errorf("failed to get free port")
-	}
-}
-
-func TestWaitFor(t *testing.T) {
-	ok := WaitFor(func() bool { return true }, 20*time.Millisecond)
-	if !ok {
-		t.Errorf("WaitFor(true) timed out")
-	}
-
-	ok = WaitFor(func() bool { return false }, 20*time.Millisecond)
-	if ok {
-		t.Errorf("WaitFor(false) worked")
+	if string(data) != "chau" {
+		t.Errorf("file content: got %q, expected %q", data, "chau")
 	}
 }
 
 func TestGenerateCert(t *testing.T) {
-	dir := MustTempDir(t)
-	defer os.RemoveAll(dir)
-	conf, err := GenerateCert(dir)
+	conf, err := GenerateCert(t.TempDir())
 	if err != nil {
 		t.Errorf("GenerateCert returned error: %v", err)
 	}