diff --git a/include/co/fs.h b/include/co/fs.h
index 88b7d8dfb..6bf6bc091 100644
--- a/include/co/fs.h
+++ b/include/co/fs.h
@@ -177,8 +177,12 @@ class __coapi file {
         return this->write(&c, 1);
     }
 
+    // if open() fails, the posix errno is stored and can be used later.
+    int open_errno() const { return _open_errno; }
+
   private:
     void* _p;
+    int _open_errno = 0;
 };
 
 // open mode:
diff --git a/include/co/unitest.h b/include/co/unitest.h
index 9eeb5f707..291054927 100644
--- a/include/co/unitest.h
+++ b/include/co/unitest.h
@@ -17,7 +17,7 @@ namespace xx {
 
 struct Failed {
     Failed(const char* c, const char* file, int line, fastring&& msg)
-        : file(file), line(line), c(c), msg(std::move(msg)) {
+        : c(c), file(file), line(line), msg(std::move(msg)) {
     }
     const char* c; // case name
     const char* file;
diff --git a/src/fs.cc b/src/fs.cc
index d3f8f4db2..ec51140e5 100644
--- a/src/fs.cc
+++ b/src/fs.cc
@@ -173,7 +173,12 @@ bool file::open(const char* path, char mode) {
     }
 
     p->fd = xx::open(path, mode);
-    return p->fd != nullfd;
+    if (p->fd != nullfd) {
+        return true;
+    } else {
+        this->_open_errno = errno;
+        return false;
+    };
 }
 
 void file::close() {
diff --git a/src/log/log.cc b/src/log/log.cc
index 1ab1d954c..af3d7539f 100644
--- a/src/log/log.cc
+++ b/src/log/log.cc
@@ -654,7 +654,7 @@ fs::file& LogFile::open(const char* topic, int level, LogTime* t) {
 
     if (!_file) {
         s.clear();
-        s << "cann't open the file: " << _path << '\n';
+        s << "cann't open the file: " << _path << ", " << strerror(_file.open_errno()) << "\n";
         log2stderr(s.data(), s.size());
     }
     return _file;
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 62d6b2d6e..ee1ffd30e 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -1,9 +1,10 @@
 file(GLOB_RECURSE ALL_TEST_FILES "*.cc")
 
+set(NON_STANDALONE_TESTS "http_serv.cc" "rpc.cc" "udp.cc" "ssl.cc" "stack.cc")
+
 foreach(TEST_FILE ${ALL_TEST_FILES})
     get_filename_component(TEST_FILE_NAME ${TEST_FILE} NAME)
     string(REPLACE ".cc" "" TEST_TARGET ${TEST_FILE_NAME})
-    message("  - ${TEST_FILE} --> ${TEST_TARGET}")
 
     add_executable(${TEST_TARGET}_test ${TEST_FILE})
 
@@ -13,5 +14,12 @@ foreach(TEST_FILE ${ALL_TEST_FILES})
 
     target_link_libraries(${TEST_TARGET}_test PRIVATE co)
 
-    add_test(NAME ${TEST_TARGET}_test COMMAND ${TEST_TARGET}_test)
+    list(FIND {NON_STANDALONE_TESTS TEST_FILE NOT_A_TEST)
+
+    if (${TEST_FILE_NAME} IN_LIST NON_STANDALONE_TESTS)
+      message("  - ${TEST_FILE} --> standalone test ${TEST_TARGET}")
+    else()
+      message("  - ${TEST_FILE} --> ${TEST_TARGET}")
+      add_test(NAME ${TEST_TARGET}_test COMMAND ${TEST_TARGET}_test)
+    endif()
 endforeach(TEST_FILE ${ALL_TEST_FILES})
diff --git a/test/mem.cc b/test/mem.cc
index 3da8826fa..84e01ec2d 100644
--- a/test/mem.cc
+++ b/test/mem.cc
@@ -6,6 +6,8 @@ DEF_int32(m, 200, "m");
 DEF_int32(t, 1, "thread num");
 DEF_bool(xfree, false, "test xfree");
 
+co::WaitGroup wg;
+
 void test_fun(int id) {
     int N = FLG_n;
     co::array<void*> v(N);
@@ -67,6 +69,7 @@ void test_fun(int id) {
 
     COUT << "thread " << id << ":\n" << s;
     v.reset();
+    wg.done();
 }
 
 void test_string() {
@@ -228,6 +231,8 @@ void test_xfree() {
             co::sleep(1);
         }
     }
+
+    wg.done();
 }
 
 int main(int argc, char** argv) {
@@ -240,14 +245,16 @@ int main(int argc, char** argv) {
         test_unordered_map();
 
         for (int i = 0; i < FLG_t; ++i) {
+            wg.add();
             std::thread(test_fun, i).detach();
         }
     } else {
+        wg.add();
         go(test_xalloc);
         go(test_xfree);
     }
 
-    while (true) sleep::sec(8);
+    wg.wait();
 
     return 0;
 }
diff --git a/test/nco.cc b/test/nco.cc
index ba9240371..4d101f444 100644
--- a/test/nco.cc
+++ b/test/nco.cc
@@ -1,15 +1,20 @@
-#include "co/co.h"
+#include "co/all.h"
 
 DEF_uint32(n, 1000000, "coroutine number");
-DEF_uint32(t, 60, "seconds to sleep in coroutines");
+DEF_uint32(t, 1, "seconds to sleep in coroutines");
+
+co::wait_group wg;
 
 DEF_main(argc, argv) {
+    COUT << "sleep " << FLG_t << " seconds\n";
     for (int i = 0; i < FLG_n; ++i) {
+        wg.add();
         go([](){
             co::sleep(FLG_t * 1000);
+            wg.done();
         });
     }
 
-    co::sleep(1000000);
+    wg.wait();
     return 0;
 }
diff --git a/test/so/easy.cc b/test/so/easy.cc
index a5aa7d810..9a6d15328 100644
--- a/test/so/easy.cc
+++ b/test/so/easy.cc
@@ -1,12 +1,22 @@
-#include "co/flag.h"
-#include "co/http.h"
+#include "co/all.h"
 
 DEF_string(d, ".", "root dir");
 DEF_string(ip, "0.0.0.0", "http server ip");
-DEF_int32(port, 80, "http server port");
+DEF_int32(port, 8080, "http server port");
 
 int main(int argc, char** argv) {
     flag::init(argc, argv);
+    go([]() {
+      co::sleep(1000);
+      http::Client c("https://github.com");
+      c.get("/");
+      int http_status = c.status();
+      CHECK_EQ(http_status, 200);
+      COUT << "http client staus: " << http_status << " OK";
+      exit(0);
+    });
+
+    COUT << "http server on http://" << FLG_ip << ":" << FLG_port;
     so::easy(FLG_d.c_str(), FLG_ip.c_str(), FLG_port); // mum never have to worry again
     return 0;
 }
diff --git a/test/so/echo.cc b/test/so/echo.cc
index 2c7eb7d7b..f02f12c56 100644
--- a/test/so/echo.cc
+++ b/test/so/echo.cc
@@ -2,12 +2,13 @@
 
 DEF_string(ip, "127.0.0.1", "ip");
 DEF_int32(port, 9988, "port");
-DEF_int32(c, 0, "client num");
+DEF_int32(c, -256, "client num: c = 0, run server only; c > 0, run client only with |c| connections; c < 0, run both server and client, with |c| client connections.");
 DEF_int32(l, 4096, "message length");
-DEF_int32(t, 60, "test time in seconds");
+DEF_int32(t, 10, "test time in seconds");
 
 void conn_cb(tcp::Connection conn) {
     fastream buf(FLG_l);
+    buf.resize(FLG_l);
 
     while (true) {
         int r = conn.recvn(&buf[0], FLG_l);
@@ -64,24 +65,39 @@ void client_fun(int i) {
 int main(int argc, char** argv) {
     flag::init(argc, argv);
 
-    if (FLG_c <= 0) {
+    if (FLG_c == 0) {
         tcp::Server().on_connection(conn_cb).start(
             FLG_ip.c_str(), FLG_port 
         );
         while (true) sleep::sec(102400);
     } else {
-        g_count = (Count*) co::zalloc(sizeof(Count) * FLG_c);
-        for (int i = 0; i < FLG_c; ++i) {
+        int num = FLG_c;
+        if (FLG_c < 0) {
+          tcp::Server().on_connection(conn_cb).start(
+              FLG_ip.c_str(), FLG_port 
+          );
+          sleep::sec(1);
+          num = -FLG_c;
+        }
+
+        g_count = (Count*) co::zalloc(sizeof(Count) * num);
+        for (int i = 0; i < num; ++i) {
             go(client_fun, i);
         }
 
-        sleep::sec(FLG_t);
+        COUT << "stress test the server with " << num << " tcp connections for " << FLG_t << " seconds";
+        for (int i = 0; i < FLG_t; ++i) {
+            sleep::sec(1);
+            std::cerr << ".";
+            std::cerr.flush();
+        }
+        std::cerr << std::endl;
         atomic_store(&g_stop, true);
         sleep::sec(3);
 
         size_t rsum = 0;
         size_t ssum = 0;
-        for (int i = 0; i < FLG_c; ++i) {
+        for (int i = 0; i < num; ++i) {
             rsum += g_count[i].r;
             ssum += g_count[i].s;
         }
diff --git a/test/so/tcp2.cc b/test/so/tcp2.cc
index 35377929e..22eaeaf2f 100644
--- a/test/so/tcp2.cc
+++ b/test/so/tcp2.cc
@@ -135,6 +135,6 @@ int main(int argc, char** argv) {
     atomic_store(&g_stopped, true);
     delete gPool;
 
-    sleep::sec(5);
+    sleep::sec(1);
     return 0;
 }
diff --git a/test/stack.cc b/test/stack.cc
index 9302d656c..f03ec48ad 100644
--- a/test/stack.cc
+++ b/test/stack.cc
@@ -6,6 +6,8 @@ DEF_bool(t, false, "if true, run test in thread");
 DEF_bool(m, false, "if true, run test in main thread");
 DEF_bool(check, false, "if true, run CHECK test");
 
+co::WaitGroup wg;
+
 void a() {
     char* p = 0;
     if (FLG_check) {
@@ -13,6 +15,7 @@ void a() {
     } else {
         *p = 'c';
     }
+    wg.done();
 }
 
 void b() {
@@ -26,6 +29,7 @@ void c() {
 int main(int argc, char** argv) {
     flag::init(argc, argv);
 
+    wg.add();
     if (FLG_m) {
         c();
     } else if (FLG_t) {
@@ -34,7 +38,6 @@ int main(int argc, char** argv) {
         go(c);
     }
 
-    while (1) sleep::sec(1024);
-
+    wg.wait();
     return 0;
 }
diff --git a/test/tw.cc b/test/tw.cc
index 4b3ec7f4e..58f34332e 100644
--- a/test/tw.cc
+++ b/test/tw.cc
@@ -317,7 +317,6 @@ const char* p;
     BM_group(reverse_search) {
         int64 v;
         size_t r;
-        const char* t;
 
         BM_add(RQS)(
             v = RQS(s, p);