test(ircserver): cover VERSION/ADMIN/TIME under the default empty SERVER_NAME

Both wire test environments hardcoded ServerName: "test.irc", so no test
exercised the shipped default and the empty server-name parameter went
unnoticed for five rework rounds. Parameterize the env's server name and
add a wire test that runs with it empty, asserting the numerics name
"neoirc" and contain no empty parameter. Verified to fail against the
pre-fix handlers.

internal/ircserver/integration_test.go

@@ -1241,3 +1241,80 @@ func TestIntegrationThirdClientObserver(t *testing.T) {
 		"carol receives trio message",
 	)
 }
+
+// assertNoEmptyParam fails if any line contains a doubled
+// space, which is what FormatMessage emits for an empty
+// non-trailing parameter.  A numeric whose server-name
+// parameter came out empty is malformed on the wire even
+// though it still contains the numeric code, so the other
+// assertions in this file would not catch it.
+func assertNoEmptyParam(
+	t *testing.T,
+	lines []string,
+	context string,
+) {
+	t.Helper()
+
+	for _, line := range lines {
+		if strings.Contains(line, "  ") {
+			t.Errorf(
+				"%s: empty parameter in wire line: %q",
+				context, line,
+			)
+		}
+	}
+}
+
+// TestIntegrationDefaultServerNameFallback runs the wire
+// server with SERVER_NAME unset, which is the shipped
+// default from config.go, and verifies that VERSION, ADMIN
+// and TIME fall back to "neoirc" exactly as the HTTP path
+// does instead of emitting an empty server-name parameter.
+//
+// Every other wire test hardcodes ServerName: "test.irc",
+// so none of them exercise the default configuration.
+func TestIntegrationDefaultServerNameFallback(t *testing.T) {
+	t.Parallel()
+
+	env := newTestEnvWithServerName(t, "")
+
+	alice := env.dial(t)
+	alice.register("alice")
+
+	alice.send("VERSION")
+
+	versionReply := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 351 ")
+	})
+	assertNoEmptyParam(t, versionReply, "VERSION")
+	assertContains(
+		t, versionReply, "neoirc",
+		"VERSION falls back to default server name",
+	)
+
+	alice.send("ADMIN")
+
+	adminReply := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 259 ")
+	})
+	assertNoEmptyParam(t, adminReply, "ADMIN")
+	assertContains(
+		t, adminReply, " 256 alice neoirc ",
+		"RPL_ADMINME names the default server",
+	)
+	assertContains(
+		t, adminReply, "admin@neoirc",
+		"RPL_ADMINEMAIL is a well-formed address",
+	)
+
+	alice.send("TIME")
+
+	timeReply := alice.readUntil(func(l string) bool {
+		return strings.Contains(l, " 391 ")
+	})
+	assertNoEmptyParam(t, timeReply, "TIME")
+	assertContains(
+		t, timeReply, " 391 alice neoirc ",
+		"RPL_TIME names the default server",
+	)
+}

internal/ircserver/server_test.go

@@ -38,6 +38,20 @@ type testEnv struct {
 func newTestEnv(t *testing.T) *testEnv {
 	t.Helper()
 
+	return newTestEnvWithServerName(t, "test.irc")
+}
+
+// newTestEnvWithServerName creates a test environment with
+// an explicit SERVER_NAME. Passing "" exercises the shipped
+// default from config.go, under which the server must fall
+// back to "neoirc" rather than emitting an empty
+// server-name parameter.
+func newTestEnvWithServerName(
+	t *testing.T,
+	serverName string,
+) *testEnv {
+	t.Helper()
+
 	dsn := fmt.Sprintf(
 		"file:%s?mode=memory&cache=shared&_journal_mode=WAL",
 		t.Name(),
@@ -67,7 +81,7 @@ func newTestEnv(t *testing.T) *testEnv {
 	brk := broker.New()
 
 	cfg := &config.Config{ //nolint:exhaustruct
-		ServerName: "test.irc",
+		ServerName: serverName,
 		MOTD:       "Welcome to test IRC",
 	}