test(build):collect llgo test ./... output to test

internal/build/build_test.go

@@ -4,7 +4,9 @@
 package build
 
 import (
+	"bytes"
 	"fmt"
+	"io"
 	"os"
 	"testing"
 
@@ -58,10 +60,36 @@ func TestRun(t *testing.T) {
 }
 
 func TestTest(t *testing.T) {
-	// fixme:with builtin package test in a llgo test ./... will cause duplicate symbol error
+	// FIXME(zzy): with builtin package test in a llgo test ./... will cause duplicate symbol error
 	mockRun([]string{"../../cl/_testgo/runtest"}, &Config{Mode: ModeTest})
 }
 
+func TestExtest(t *testing.T) {
+	originalStdout := os.Stdout
+	defer func() { os.Stdout = originalStdout }()
+
+	r, w, err := os.Pipe()
+	if err != nil {
+		t.Fatalf("os.Pipe failed: %v", err)
+	}
+	os.Stdout = w
+	outputChan := make(chan string)
+	go func() {
+		var data bytes.Buffer
+		io.Copy(&data, r)
+		outputChan <- data.String()
+	}()
+
+	mockRun([]string{"../../cl/_testgo/runextest/..."}, &Config{Mode: ModeTest})
+
+	w.Close()
+	got := <-outputChan
+	expected := "PASS\nPASS\nPASS\nPASS\n"
+	if got != expected {
+		t.Errorf("Expected output %q, but got %q", expected, got)
+	}
+}
+
 func TestCmpTest(t *testing.T) {
 	mockRun([]string{"../../cl/_testgo/runtest"}, &Config{Mode: ModeCmpTest})
 }