A minor refactoring of the way the test infrastructure gets the FileSystem implementation for integration tests.

--
PiperOrigin-RevId: 146114082
MOS_MIGRATED_REVID=146114082
diff --git a/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java b/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
index d994756..64ede46 100644
--- a/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
+++ b/src/test/java/com/google/devtools/build/lib/testutil/TestConstants.java
@@ -63,6 +63,9 @@
       "com.google.devtools.build.lib.bazel.rules.BazelRuleClassProvider";
   public static final String TEST_RULE_MODULE =
         "com.google.devtools.build.lib.bazel.rules.BazelRulesModule";
+  public static final String TEST_REAL_UNIX_FILE_SYSTEM =
+      "com.google.devtools.build.lib.vfs.UnixFileSystem";
+
   public static final ImmutableList<String> IGNORED_MESSAGE_PREFIXES = ImmutableList.<String>of();
 
   public static final String GCC_INCLUDE_PATH = "external/bazel_tools/tools/cpp/gcc3";
diff --git a/src/test/java/com/google/devtools/build/lib/vfs/util/FileSystems.java b/src/test/java/com/google/devtools/build/lib/vfs/util/FileSystems.java
index 9329a8b..1da3198 100644
--- a/src/test/java/com/google/devtools/build/lib/vfs/util/FileSystems.java
+++ b/src/test/java/com/google/devtools/build/lib/vfs/util/FileSystems.java
@@ -15,6 +15,7 @@
 
 import com.google.common.base.Verify;
 import com.google.devtools.build.lib.concurrent.ThreadSafety.ThreadSafe;
+import com.google.devtools.build.lib.testutil.TestConstants;
 import com.google.devtools.build.lib.util.OS;
 import com.google.devtools.build.lib.vfs.FileSystem;
 import com.google.devtools.build.lib.vfs.JavaIoFileSystem;
@@ -55,7 +56,12 @@
       }
     } else {
       if (defaultNativeFileSystem == null) {
-        defaultNativeFileSystem = new UnixFileSystem();
+        try {
+          defaultNativeFileSystem = (FileSystem)
+              Class.forName(TestConstants.TEST_REAL_UNIX_FILE_SYSTEM).newInstance();
+        } catch (Exception e) {
+          throw new IllegalStateException(e);
+        }
       } else {
         Verify.verify(defaultNativeFileSystem instanceof UnixFileSystem);
       }