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diff --git a/jimfs/src/test/java/com/google/common/jimfs/HeapDiskTest.java b/jimfs/src/test/java/com/google/common/jimfs/HeapDiskTest.java
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+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.google.common.jimfs;
+
+import static com.google.common.truth.Truth.assertThat;
+import static org.junit.Assert.fail;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+import org.junit.Before;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+/**
+ * Tests for {@link HeapDisk}.
+ *
+ * @author Colin Decker
+ */
+@RunWith(JUnit4.class)
+public class HeapDiskTest {
+
+  private RegularFile blocks;
+
+  @Before
+  public void setUp() {
+    // the HeapDisk of this file is unused; it's passed to other HeapDisks to test operations
+    blocks = RegularFile.create(-1, new HeapDisk(2, 2, 2));
+  }
+
+  @Test
+  public void testInitialSettings_basic() {
+    HeapDisk disk = new HeapDisk(8192, 100, 100);
+
+    assertThat(disk.blockSize()).isEqualTo(8192);
+    assertThat(disk.getTotalSpace()).isEqualTo(819200);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(819200);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(0);
+  }
+
+  @Test
+  public void testInitialSettings_fromConfiguration() {
+    Configuration config =
+        Configuration.unix().toBuilder()
+            .setBlockSize(4)
+            .setMaxSize(99) // not a multiple of 4
+            .setMaxCacheSize(25)
+            .build();
+
+    HeapDisk disk = new HeapDisk(config);
+
+    assertThat(disk.blockSize()).isEqualTo(4);
+    assertThat(disk.getTotalSpace()).isEqualTo(96);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(96);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(0);
+  }
+
+  @Test
+  public void testAllocate() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 0);
+
+    disk.allocate(blocks, 1);
+
+    assertThat(blocks.blockCount()).isEqualTo(1);
+    assertThat(blocks.getBlock(0).length).isEqualTo(4);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(36);
+
+    disk.allocate(blocks, 5);
+
+    assertThat(blocks.blockCount()).isEqualTo(6);
+    for (int i = 0; i < blocks.blockCount(); i++) {
+      assertThat(blocks.getBlock(i).length).isEqualTo(4);
+    }
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(16);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(0);
+  }
+
+  @Test
+  public void testFree_noCaching() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 0);
+    disk.allocate(blocks, 6);
+
+    disk.free(blocks, 2);
+    assertThat(blocks.blockCount()).isEqualTo(4);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(24);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(0);
+
+    disk.free(blocks);
+
+    assertThat(blocks.blockCount()).isEqualTo(0);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(40);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(0);
+  }
+
+  @Test
+  public void testFree_fullCaching() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 10);
+    disk.allocate(blocks, 6);
+
+    disk.free(blocks, 2);
+
+    assertThat(blocks.blockCount()).isEqualTo(4);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(24);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(2);
+
+    disk.free(blocks);
+
+    assertThat(blocks.blockCount()).isEqualTo(0);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(40);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(6);
+  }
+
+  @Test
+  public void testFree_partialCaching() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 4);
+    disk.allocate(blocks, 6);
+
+    disk.free(blocks, 2);
+
+    assertThat(blocks.blockCount()).isEqualTo(4);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(24);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(2);
+
+    disk.free(blocks);
+
+    assertThat(blocks.blockCount()).isEqualTo(0);
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(40);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(4);
+  }
+
+  @Test
+  public void testAllocateFromCache_fullAllocationFromCache() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 10);
+    disk.allocate(blocks, 10);
+
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(0);
+
+    disk.free(blocks);
+
+    assertThat(blocks.blockCount()).isEqualTo(0);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(10);
+
+    List<byte[]> cachedBlocks = new ArrayList<>();
+    for (int i = 0; i < 10; i++) {
+      cachedBlocks.add(disk.blockCache.getBlock(i));
+    }
+
+    disk.allocate(blocks, 6);
+
+    assertThat(blocks.blockCount()).isEqualTo(6);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(4);
+
+    // the 6 arrays in blocks are the last 6 arrays that were cached
+    for (int i = 0; i < 6; i++) {
+      assertThat(blocks.getBlock(i)).isEqualTo(cachedBlocks.get(i + 4));
+    }
+  }
+
+  @Test
+  public void testAllocateFromCache_partialAllocationFromCache() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 4);
+    disk.allocate(blocks, 10);
+
+    assertThat(disk.getUnallocatedSpace()).isEqualTo(0);
+
+    disk.free(blocks);
+
+    assertThat(blocks.blockCount()).isEqualTo(0);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(4);
+
+    List<byte[]> cachedBlocks = new ArrayList<>();
+    for (int i = 0; i < 4; i++) {
+      cachedBlocks.add(disk.blockCache.getBlock(i));
+    }
+
+    disk.allocate(blocks, 6);
+
+    assertThat(blocks.blockCount()).isEqualTo(6);
+    assertThat(disk.blockCache.blockCount()).isEqualTo(0);
+
+    // the last 4 arrays in blocks are the 4 arrays that were cached
+    for (int i = 2; i < 6; i++) {
+      assertThat(blocks.getBlock(i)).isEqualTo(cachedBlocks.get(i - 2));
+    }
+  }
+
+  @Test
+  public void testFullDisk() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 4);
+    disk.allocate(blocks, 10);
+
+    try {
+      disk.allocate(blocks, 1);
+      fail();
+    } catch (IOException expected) {
+    }
+  }
+
+  @Test
+  public void testFullDisk_doesNotAllocatePartiallyWhenTooManyBlocksRequested() throws IOException {
+    HeapDisk disk = new HeapDisk(4, 10, 4);
+    disk.allocate(blocks, 6);
+
+    RegularFile blocks2 = RegularFile.create(-2, disk);
+
+    try {
+      disk.allocate(blocks2, 5);
+      fail();
+    } catch (IOException expected) {
+    }
+
+    assertThat(blocks2.blockCount()).isEqualTo(0);
+  }
+}