simpleperf: fix test for vdso file.

The kernel may export vdso file with no symbols.

Bug: http://b/69073856
Test: run simpleperf_unit_test.
Change-Id: I5c59513debe014ffd7fd772be110044eefcbb37f
diff --git a/simpleperf/environment_test.cpp b/simpleperf/environment_test.cpp
index 4891467..25eee96 100644
--- a/simpleperf/environment_test.cpp
+++ b/simpleperf/environment_test.cpp
@@ -17,6 +17,7 @@
 #include <gtest/gtest.h>
 
 #include <android-base/file.h>
+#include <android-base/test_utils.h>
 
 #include "dso.h"
 #include "environment.h"
@@ -35,10 +36,11 @@
     // Vdso isn't used, no need to test.
     return;
   }
+  TemporaryDir tmpdir;
+  SetTempDirectoryUsedInRecording(tmpdir.path);
   PrepareVdsoFile();
   std::unique_ptr<Dso> dso = Dso::CreateDso(DSO_ELF_FILE, "[vdso]",
                                             sizeof(size_t) == sizeof(uint64_t));
   ASSERT_TRUE(dso != nullptr);
-  const std::vector<Symbol>& symbols = dso->GetSymbols();
-  ASSERT_FALSE(symbols.empty());
+  ASSERT_NE(dso->GetDebugFilePath(), "[vdso]");
 }