[script] use real time when run expect tests (#5130)

script/test

@@ -44,7 +44,6 @@ readonly NODE_TYPE="${NODE_TYPE:-sim}"
 readonly OT_NATIVE_IP="${OT_NATIVE_IP:-0}"
 readonly THREAD_VERSION="${THREAD_VERSION:-1.1}"
 readonly VERBOSE="${VERBOSE:-0}"
-readonly VIRTUAL_TIME="${VIRTUAL_TIME:-1}"
 
 build_simulation()
 {
@@ -347,6 +346,18 @@ envsetup()
         fi
     fi
 
+    if [[ ! ${VIRTUAL_TIME+x} ]]; then
+        # All expect tests only works in real time mode.
+        VIRTUAL_TIME=1
+        for arg in "$@"; do
+            if [[ $arg == expect ]]; then
+                VIRTUAL_TIME=0
+                break
+            fi
+        done
+    fi
+
+    readonly VIRTUAL_TIME
     export NODE_TYPE VIRTUAL_TIME
 
     # CMake always works in verbose mode if VERBOSE exists in environments.
@@ -365,7 +376,7 @@ envsetup()
 
 main()
 {
-    envsetup
+    envsetup "$@"
 
     if [[ -z $1 ]]; then
         print_usage 1