diff --git a/tests/testapk/Android.bp b/tests/testapk/Android.bp
index 1122b25..fdc95de 100644
--- a/tests/testapk/Android.bp
+++ b/tests/testapk/Android.bp
@@ -13,13 +13,19 @@
 // TODO(jiyong): make this a binary, not a shared library
 cc_library_shared {
     name: "MicrodroidTestNativeLib",
-    srcs: ["src/native/*.cpp"],
+    srcs: ["src/native/testbinary.cpp"],
     shared_libs: [
         "android.system.keystore2-V1-ndk_platform",
         "libbinder_ndk",
+        "MicrodroidTestNativeLibSub",
     ],
 }
 
+cc_library_shared {
+    name: "MicrodroidTestNativeLibSub",
+    srcs: ["src/native/testlib.cpp"],
+}
+
 genrule {
     name: "MicrodroidTestApp.signed",
     out: [
@@ -27,12 +33,12 @@
         "MicrodroidTestApp.apk.idsig",
     ],
     srcs: [":MicrodroidTestApp"],
-    tools:["apksigner"],
+    tools: ["apksigner"],
     tool_files: ["test.keystore"],
     cmd: "$(location apksigner) sign " +
-         "--ks $(location test.keystore) " +
-         "--ks-pass=pass:testkey --key-pass=pass:testkey " +
-         "--in $(in) " +
-         "--out $(genDir)/MicrodroidTestApp.apk",
-         // $(genDir)/MicrodroidTestApp.apk.idsig is generated implicitly
+        "--ks $(location test.keystore) " +
+        "--ks-pass=pass:testkey --key-pass=pass:testkey " +
+        "--in $(in) " +
+        "--out $(genDir)/MicrodroidTestApp.apk",
+    // $(genDir)/MicrodroidTestApp.apk.idsig is generated implicitly
 }
diff --git a/tests/testapk/src/native/testbinary.cpp b/tests/testapk/src/native/testbinary.cpp
index 682ab2a..9bd594b 100644
--- a/tests/testapk/src/native/testbinary.cpp
+++ b/tests/testapk/src/native/testbinary.cpp
@@ -24,6 +24,8 @@
 using aidl::android::system::keystore2::IKeystoreSecurityLevel;
 using aidl::android::system::keystore2::IKeystoreService;
 
+extern void testlib_sub();
+
 namespace {
 
 bool test_keystore() {
@@ -52,6 +54,7 @@
             printf(" ");
         }
     }
+    testlib_sub();
     printf("\n");
 
     __system_property_set("debug.microdroid.app.run", "true");
diff --git a/tests/testapk/src/native/testlib.cpp b/tests/testapk/src/native/testlib.cpp
new file mode 100644
index 0000000..792c6c8
--- /dev/null
+++ b/tests/testapk/src/native/testlib.cpp
@@ -0,0 +1,5 @@
+#include <sys/system_properties.h>
+
+void testlib_sub() {
+    __system_property_set("debug.microdroid.app.sublib.run", "true");
+}