cmd/devp2p, internal/utesting: implement TAP output (#21760)

TAP is a text format for test results. Parsers for it are available in many languages,
making it easy to consume. I want TAP output from our protocol tests because the
Hive wrapper around them needs to know about the test names and their individual
results and logs. It would also be possible to just write this info as JSON, but I don't
want to invent a new format.

This also improves the normal console output for tests (when running without --tap).
It now prints -- RUN lines before any output from the test, and indents the log output
by one space.

internal/utesting/utesting_test.go

@@ -17,6 +17,8 @@
 package utesting
 
 import (
+	"bytes"
+	"regexp"
 	"strings"
 	"testing"
 )
@@ -53,3 +55,85 @@ func TestTest(t *testing.T) {
 		t.Fatalf("wrong result for panicking test: %#v", results[2])
 	}
 }
+
+var outputTests = []Test{
+	{
+		Name: "TestWithLogs",
+		Fn: func(t *T) {
+			t.Log("output line 1")
+			t.Log("output line 2\noutput line 3")
+		},
+	},
+	{
+		Name: "TestNoLogs",
+		Fn:   func(t *T) {},
+	},
+	{
+		Name: "FailWithLogs",
+		Fn: func(t *T) {
+			t.Log("output line 1")
+			t.Error("failed 1")
+		},
+	},
+	{
+		Name: "FailMessage",
+		Fn: func(t *T) {
+			t.Error("failed 2")
+		},
+	},
+	{
+		Name: "FailNoOutput",
+		Fn: func(t *T) {
+			t.Fail()
+		},
+	},
+}
+
+func TestOutput(t *testing.T) {
+	var buf bytes.Buffer
+	RunTests(outputTests, &buf)
+
+	want := regexp.MustCompile(`
+^-- RUN TestWithLogs
+ output line 1
+ output line 2
+ output line 3
+-- OK TestWithLogs \([^)]+\)
+-- OK TestNoLogs \([^)]+\)
+-- RUN FailWithLogs
+ output line 1
+ failed 1
+-- FAIL FailWithLogs \([^)]+\)
+-- RUN FailMessage
+ failed 2
+-- FAIL FailMessage \([^)]+\)
+-- FAIL FailNoOutput \([^)]+\)
+2/5 tests passed.
+$`[1:])
+	if !want.MatchString(buf.String()) {
+		t.Fatalf("output does not match: %q", buf.String())
+	}
+}
+
+func TestOutputTAP(t *testing.T) {
+	var buf bytes.Buffer
+	RunTAP(outputTests, &buf)
+
+	want := `
+1..5
+ok 1 TestWithLogs
+# output line 1
+# output line 2
+# output line 3
+ok 2 TestNoLogs
+not ok 3 FailWithLogs
+# output line 1
+# failed 1
+not ok 4 FailMessage
+# failed 2
+not ok 5 FailNoOutput
+`
+	if buf.String() != want[1:] {
+		t.Fatalf("output does not match: %q", buf.String())
+	}
+}