LUCENE-6989: Fix some tests that hardcode MMapDirectory (and also the FSDirectory randomizer), to only use MMapDirectory on Windows, if it supports unmapping. Otherwise tests will fail.

lucene/core/src/test/org/apache/lucene/index/Test4GBStoredFields.java

@@ -41,6 +41,8 @@ public class Test4GBStoredFields extends LuceneTestCase {
 
   @Nightly
   public void test() throws Exception {
+    assumeWorkingMMapOnWindows();
+    
     MockDirectoryWrapper dir = new MockDirectoryWrapper(random(), new MMapDirectory(createTempDir("4GBStoredFields")));
     dir.setThrottling(MockDirectoryWrapper.Throttling.NEVER);
 

lucene/core/src/test/org/apache/lucene/index/TestIndexWriter.java

@@ -1251,8 +1251,9 @@ public class TestIndexWriter extends LuceneTestCase {
 
 
   public void testDeleteUnusedFiles() throws Exception {
-
     assumeFalse("test relies on exact filenames", Codec.getDefault() instanceof SimpleTextCodec);
+    assumeWorkingMMapOnWindows();
+    
     for(int iter=0;iter<2;iter++) {
       // relies on windows semantics
       Path path = createTempDir();

lucene/core/src/test/org/apache/lucene/store/TestDirectory.java

@@ -20,6 +20,7 @@ package org.apache.lucene.store;
 import java.io.IOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
 
@@ -37,11 +38,13 @@ public class TestDirectory extends LuceneTestCase {
       largeBuffer[i] = (byte) i; // automatically loops with modulo
     }
 
-    final FSDirectory[] dirs = new FSDirectory[] {
-      new SimpleFSDirectory(path),
-      new NIOFSDirectory(path),
-      new MMapDirectory(path)
-    };
+    final List<FSDirectory> dirs0 = new ArrayList<>();
+    dirs0.add(new SimpleFSDirectory(path));
+    dirs0.add(new NIOFSDirectory(path));
+    if (hasWorkingMMapOnWindows()) {
+      dirs0.add(new MMapDirectory(path));
+    }
+    final FSDirectory[] dirs = dirs0.stream().toArray(FSDirectory[]::new);
 
     for (int i=0; i<dirs.length; i++) {
       FSDirectory dir = dirs[i];

lucene/core/src/test/org/apache/lucene/store/TestMmapDirectory.java

@@ -39,8 +39,7 @@ public class TestMmapDirectory extends BaseDirectoryTestCase {
   @Override
   public void setUp() throws Exception {
     super.setUp();
-    assumeTrue("test requires a jre that supports unmapping: " + MMapDirectory.UNMAP_NOT_SUPPORTED_REASON,
-        MMapDirectory.UNMAP_SUPPORTED);
+    assumeTrue(MMapDirectory.UNMAP_NOT_SUPPORTED_REASON, MMapDirectory.UNMAP_SUPPORTED);
   }
   
   @Ignore("This test is for JVM testing purposes. There are no guarantees that it may not fail with SIGSEGV!")

lucene/core/src/test/org/apache/lucene/store/TestMultiMMap.java

@@ -46,8 +46,7 @@ public class TestMultiMMap extends BaseDirectoryTestCase {
   @Override
   public void setUp() throws Exception {
     super.setUp();
-    assumeTrue("test requires a jre that supports unmapping: " + MMapDirectory.UNMAP_NOT_SUPPORTED_REASON,
-        MMapDirectory.UNMAP_SUPPORTED);
+    assumeTrue(MMapDirectory.UNMAP_NOT_SUPPORTED_REASON, MMapDirectory.UNMAP_SUPPORTED);
   }
   
   public void testCloneSafety() throws Exception {

lucene/core/src/test/org/apache/lucene/util/fst/Test2BFST.java

@@ -40,6 +40,8 @@ public class Test2BFST extends LuceneTestCase {
   private static long LIMIT = 3L*1024*1024*1024;
 
   public void test() throws Exception {
+    assumeWorkingMMapOnWindows();
+    
     int[] ints = new int[7];
     IntsRef input = new IntsRef(ints, 0, ints.length);
     long seed = random().nextLong();

lucene/test-framework/src/java/org/apache/lucene/index/BaseStoredFieldsFormatTestCase.java

@@ -663,6 +663,8 @@ public abstract class BaseStoredFieldsFormatTestCase extends BaseIndexFileFormat
 
   @Nightly
   public void testBigDocuments() throws IOException {
+    assumeWorkingMMapOnWindows();
+    
     // "big" as "much bigger than the chunk size"
     // for this test we force a FS dir
     // we can't just use newFSDirectory, because this test doesn't really index anything.

lucene/test-framework/src/java/org/apache/lucene/util/LuceneTestCase.java

@@ -94,6 +94,7 @@ import org.apache.lucene.store.FSLockFactory;
 import org.apache.lucene.store.FlushInfo;
 import org.apache.lucene.store.IOContext;
 import org.apache.lucene.store.LockFactory;
+import org.apache.lucene.store.MMapDirectory;
 import org.apache.lucene.store.MergeInfo;
 import org.apache.lucene.store.MockDirectoryWrapper.Throttling;
 import org.apache.lucene.store.MockDirectoryWrapper;
@@ -456,11 +457,24 @@ public abstract class LuceneTestCase extends Assert {
     LEAVE_TEMPORARY = defaultValue;
   }
 
+  /** Returns true, if MMapDirectory supports unmapping on this platform (required for Windows), or if we are not on Windows. */
+  public static boolean hasWorkingMMapOnWindows() {
+    return !Constants.WINDOWS || MMapDirectory.UNMAP_SUPPORTED;
+  }
+  
+  /** Assumes that the current MMapDirectory implementation supports unmapping, so the test will not fail on Windows.
+   * @see #hasWorkingMMapOnWindows()
+   * */
+  public static void assumeWorkingMMapOnWindows() {
+    assumeTrue(MMapDirectory.UNMAP_NOT_SUPPORTED_REASON, hasWorkingMMapOnWindows());
+  }
+
   /** Filesystem-based {@link Directory} implementations. */
   private static final List<String> FS_DIRECTORIES = Arrays.asList(
     "SimpleFSDirectory",
     "NIOFSDirectory",
-    "MMapDirectory"
+    // SimpleFSDirectory as replacement for MMapDirectory if unmapping is not supported on Windows (to make randomization stable):
+    hasWorkingMMapOnWindows() ? "MMapDirectory" : "SimpleFSDirectory"
   );
 
   /** All {@link Directory} implementations. */
@@ -469,7 +483,7 @@ public abstract class LuceneTestCase extends Assert {
     CORE_DIRECTORIES = new ArrayList<>(FS_DIRECTORIES);
     CORE_DIRECTORIES.add("RAMDirectory");
   }
-
+  
   /** A {@link org.apache.lucene.search.QueryCachingPolicy} that randomly caches. */
   public static final QueryCachingPolicy MAYBE_CACHE_POLICY = new QueryCachingPolicy() {
 
@@ -853,7 +867,7 @@ public abstract class LuceneTestCase extends Assert {
   public static void assumeNoException(String msg, Exception e) {
     RandomizedTest.assumeNoException(msg, e);
   }
-
+  
   /**
    * Return <code>args</code> as a {@link Set} instance. The order of elements is not
    * preserved in iterators.