Fix several off-by-one issues in UploadFileMessage

We now fuzz UploadFileMessage, generating random files and checking they
round-trip correctly.

The joy of having a long-lasting refactor branch with an absolutely
massive diff, is that you end up spotting bugs, and then it's a massive
pain to merge the fix back into trunk!

.gitignore

@@ -6,6 +6,7 @@
 /out
 /doc/out/
 /node_modules
+/.jqwik-database
 
 # Runtime directories
 /run

build.gradle

@@ -14,9 +14,10 @@
     id "cc-tweaked.illuaminate"
 }
 
-import org.apache.tools.ant.taskdefs.condition.Os
+
 import cc.tweaked.gradle.IlluaminateExec
 import cc.tweaked.gradle.IlluaminateExecToDir
+import org.apache.tools.ant.taskdefs.condition.Os
 
 version = mod_version
 
@@ -143,12 +144,12 @@ accessTransformer file('src/testMod/resources/META-INF/accesstransformer.cfg')
 
     shade 'org.squiddev:Cobalt:0.5.7'
 
-    testImplementation 'org.junit.jupiter:junit-jupiter-api:5.7.0'
-    testImplementation 'org.junit.jupiter:junit-jupiter-params:5.7.0'
-    testRuntimeOnly 'org.junit.jupiter:junit-jupiter-engine:5.7.0'
-    testImplementation 'org.hamcrest:hamcrest:2.2'
-    testImplementation 'org.jetbrains.kotlin:kotlin-stdlib-jdk8:1.7.0'
-    testImplementation 'org.jetbrains.kotlinx:kotlinx-coroutines-core:1.6.2'
+    testCompileOnly(libs.autoService)
+    testAnnotationProcessor(libs.autoService)
+
+    testImplementation(libs.bundles.test)
+    testImplementation(libs.bundles.kotlin)
+    testRuntimeOnly(libs.bundles.testRuntime)
 
     testModImplementation sourceSets.main.output
 

gradle/libs.versions.toml

@@ -0,0 +1,29 @@
+[versions]
+autoService = "1.0.1"
+kotlin = "1.7.10"
+kotlin-coroutines = "1.6.0"
+
+# Testing
+hamcrest = "2.2"
+jqwik = "1.7.0"
+junit = "5.9.1"
+
+[libraries]
+autoService = { module = "com.google.auto.service:auto-service", version.ref = "autoService" }
+kotlin-coroutines = { module = "org.jetbrains.kotlinx:kotlinx-coroutines-core", version.ref = "kotlin-coroutines" }
+kotlin-stdlib = { module = "org.jetbrains.kotlin:kotlin-stdlib-jdk8", version.ref = "kotlin" }
+
+# Testing
+hamcrest = { module = "org.hamcrest:hamcrest", version.ref = "hamcrest" }
+jqwik-api = { module = "net.jqwik:jqwik-api", version.ref = "jqwik" }
+jqwik-engine = { module = "net.jqwik:jqwik-engine", version.ref = "jqwik" }
+junit-jupiter-api = { module = "org.junit.jupiter:junit-jupiter-api", version.ref = "junit" }
+junit-jupiter-engine = { module = "org.junit.jupiter:junit-jupiter-engine", version.ref = "junit" }
+junit-jupiter-params = { module = "org.junit.jupiter:junit-jupiter-params", version.ref = "junit" }
+
+[bundles]
+kotlin = ["kotlin-stdlib", "kotlin-coroutines"]
+
+# Testing
+test = ["junit-jupiter-api", "junit-jupiter-params", "hamcrest", "jqwik-api"]
+testRuntime = ["junit-jupiter-engine", "jqwik-engine"]

src/main/java/dan200/computercraft/client/gui/ComputerScreenBase.java

@@ -191,7 +191,7 @@ public void onFilesDrop( @Nonnull List<Path> files )
             return;
         }
 
-        if( toUpload.size() > 0 ) UploadFileMessage.send( menu, toUpload );
+        if( toUpload.size() > 0 ) UploadFileMessage.send( menu, toUpload, NetworkHandler::sendToServer );
     }
 
     public void uploadResult( UploadResult result, ITextComponent message )

src/main/java/dan200/computercraft/shared/network/client/TerminalState.java

@@ -23,7 +23,7 @@
 
 /**
  * A snapshot of a terminal's state.
- *
+ * <p>
  * This is somewhat memory inefficient (we build a buffer, only to write it elsewhere), however it means we get a
  * complete and accurate description of a terminal, which avoids a lot of complexities with resizing terminals, dirty
  * states, etc...

src/main/java/dan200/computercraft/shared/network/server/UploadFileMessage.java

@@ -5,11 +5,11 @@
  */
 package dan200.computercraft.shared.network.server;
 
+import com.google.common.annotations.VisibleForTesting;
 import dan200.computercraft.shared.computer.menu.ComputerMenu;
 import dan200.computercraft.shared.computer.menu.ServerInputHandler;
 import dan200.computercraft.shared.computer.upload.FileSlice;
 import dan200.computercraft.shared.computer.upload.FileUpload;
-import dan200.computercraft.shared.network.NetworkHandler;
 import io.netty.handler.codec.DecoderException;
 import net.minecraft.entity.player.ServerPlayerEntity;
 import net.minecraft.inventory.container.Container;
@@ -21,6 +21,7 @@
 import java.util.ArrayList;
 import java.util.List;
 import java.util.UUID;
+import java.util.function.Consumer;
 
 public class UploadFileMessage extends ComputerServerMessage
 {
@@ -30,13 +31,13 @@ public class UploadFileMessage extends ComputerServerMessage
     public static final int MAX_FILES = 32;
     public static final int MAX_FILE_NAME = 128;
 
-    private static final int FLAG_FIRST = 1;
-    private static final int FLAG_LAST = 2;
+    static final @VisibleForTesting int FLAG_FIRST = 1;
+    static final @VisibleForTesting int FLAG_LAST = 2;
 
     private final UUID uuid;
-    private final int flag;
-    private final List<FileUpload> files;
-    private final List<FileSlice> slices;
+    final @VisibleForTesting int flag;
+    final @VisibleForTesting List<FileUpload> files;
+    final @VisibleForTesting List<FileSlice> slices;
 
     UploadFileMessage( Container menu, UUID uuid, int flag, List<FileUpload> files, List<FileSlice> slices )
     {
@@ -57,14 +58,14 @@ public UploadFileMessage( @Nonnull PacketBuffer buf )
         if( (flag & FLAG_FIRST) != 0 )
         {
             int nFiles = buf.readVarInt();
-            if( nFiles >= MAX_FILES ) throw new DecoderException( "Too many files" );
+            if( nFiles > MAX_FILES ) throw new DecoderException( "Too many files" );
 
             List<FileUpload> files = this.files = new ArrayList<>( nFiles );
             for( int i = 0; i < nFiles; i++ )
             {
                 String name = buf.readUtf( MAX_FILE_NAME );
                 int size = buf.readVarInt();
-                if( size > MAX_SIZE || (totalSize += size) >= MAX_SIZE )
+                if( size > MAX_SIZE || (totalSize += size) > MAX_SIZE )
                 {
                     throw new DecoderException( "Files are too large" );
                 }
@@ -128,7 +129,7 @@ public void toBytes( @Nonnull PacketBuffer buf )
         }
     }
 
-    public static void send( Container container, List<FileUpload> files )
+    public static void send( Container container, List<FileUpload> files, Consumer<UploadFileMessage> send )
     {
         UUID uuid = UUID.randomUUID();
 
@@ -148,7 +149,7 @@ public static void send( Container container, List<FileUpload> files )
             {
                 if( remaining <= 0 )
                 {
-                    NetworkHandler.sendToServer( first
+                    send.accept( first
                         ? new UploadFileMessage( container, uuid, FLAG_FIRST, files, new ArrayList<>( slices ) )
                         : new UploadFileMessage( container, uuid, 0, null, new ArrayList<>( slices ) ) );
                     slices.clear();
@@ -167,7 +168,7 @@ public static void send( Container container, List<FileUpload> files )
             contents.position( 0 ).limit( capacity );
         }
 
-        NetworkHandler.sendToServer( first
+        send.accept( first
             ? new UploadFileMessage( container, uuid, FLAG_FIRST | FLAG_LAST, files, new ArrayList<>( slices ) )
             : new UploadFileMessage( container, uuid, FLAG_LAST, null, new ArrayList<>( slices ) ) );
     }

src/test/java/dan200/computercraft/shared/network/server/UploadFileMessageTest.java

@@ -0,0 +1,152 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.shared.network.server;
+
+import dan200.computercraft.shared.computer.upload.FileSlice;
+import dan200.computercraft.shared.computer.upload.FileUpload;
+import dan200.computercraft.support.ArbitraryByteBuffer;
+import dan200.computercraft.support.FakeContainer;
+import io.netty.buffer.Unpooled;
+import net.jqwik.api.*;
+import net.minecraft.network.PacketBuffer;
+import org.hamcrest.Matcher;
+
+import java.nio.ByteBuffer;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static dan200.computercraft.shared.network.server.UploadFileMessage.*;
+import static dan200.computercraft.support.ByteBufferMatcher.bufferEqual;
+import static dan200.computercraft.support.ContramapMatcher.contramap;
+import static dan200.computercraft.support.CustomMatchers.containsWith;
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.*;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class UploadFileMessageTest
+{
+    /**
+     * Sends packets on a roundtrip, ensuring that their contents are reassembled on the other end.
+     *
+     * @param sentFiles The files to send.
+     */
+    @Property( tries = 500 )
+    @Tag( "slow" )
+    public void testRoundTrip( @ForAll( "fileUploads" ) List<FileUpload> sentFiles )
+    {
+        List<FileUpload> receivedFiles = receive( roundtripPackets( send( sentFiles ) ) );
+        assertThat( receivedFiles, containsWith( sentFiles, UploadFileMessageTest::uploadEqual ) );
+    }
+
+    /**
+     * "Send" our file uploads, converting them to a list of packets.
+     *
+     * @param uploads The files to send.
+     * @return The list of packets.
+     */
+    private static List<UploadFileMessage> send( List<FileUpload> uploads )
+    {
+        List<UploadFileMessage> packets = new ArrayList<>();
+        UploadFileMessage.send( new FakeContainer(), uploads, packets::add );
+        return packets;
+    }
+
+    /**
+     * Write our packets to a buffer and then read them out again.
+     *
+     * @param packets The packets to roundtrip.
+     * @return The
+     */
+    private static List<UploadFileMessage> roundtripPackets( List<UploadFileMessage> packets )
+    {
+        return packets.stream().map( packet -> {
+            PacketBuffer buffer = new PacketBuffer( Unpooled.directBuffer() );
+            packet.toBytes( buffer );
+            // We include things like file size in the packet, but not in the count, so grant a slightly larger threshold.
+            assertThat( "Packet is too large", buffer.writerIndex(), lessThanOrEqualTo( MAX_PACKET_SIZE + 128 ) );
+            if( (packet.flag & FLAG_LAST) == 0 )
+            {
+                int expectedSize = (packet.flag & FLAG_FIRST) != 0
+                    ? MAX_PACKET_SIZE - MAX_FILE_NAME * MAX_FILES
+                    : MAX_PACKET_SIZE;
+                assertThat(
+                    "Non-final packets should be efficiently packed", buffer.writerIndex(), greaterThanOrEqualTo( expectedSize )
+                );
+            }
+
+            UploadFileMessage result = new UploadFileMessage( buffer );
+
+            buffer.release();
+            assertEquals( 0, buffer.refCnt(), "Buffer should have no references" );
+
+            return result;
+        } ).collect( Collectors.toList() );
+    }
+
+    /**
+     * "Receive" our upload packets.
+     *
+     * @param packets The packets to receive. Note that this will clobber the {@link FileUpload}s in the first packet,
+     *                so you may want to copy (or {@linkplain #roundtripPackets(List) roundtrip} first.
+     * @return The consumed file uploads.
+     */
+    private static List<FileUpload> receive( List<UploadFileMessage> packets )
+    {
+        List<FileUpload> files = packets.get( 0 ).files;
+        for( int i = 0; i < packets.size(); i++ )
+        {
+            UploadFileMessage packet = packets.get( i );
+            boolean isFirst = i == 0;
+            boolean isLast = i == packets.size() - 1;
+            assertEquals( isFirst, (packet.flag & FLAG_FIRST) != 0, "FLAG_FIRST" );
+            assertEquals( isLast, (packet.flag & FLAG_LAST) != 0, "FLAG_LAST" );
+
+            for( FileSlice slice : packet.slices ) slice.apply( files );
+        }
+
+        return files;
+    }
+
+    @Provide
+    Arbitrary<FileUpload> fileUpload()
+    {
+        return Combinators.combine(
+            Arbitraries.oneOf( Arrays.asList(
+                // 1.16 doesn't correctly handle unicode file names. We'll be generous in our tests here.
+                Arbitraries.strings().ofMinLength( 1 ).ascii().ofMaxLength( MAX_FILE_NAME ),
+                Arbitraries.strings().ofMinLength( 1 ).ofMaxLength( MAX_FILE_NAME / 4 )
+            ) ),
+            ArbitraryByteBuffer.bytes().ofMaxSize( MAX_SIZE )
+        ).as( UploadFileMessageTest::file );
+    }
+
+    @Provide
+    Arbitrary<List<FileUpload>> fileUploads()
+    {
+        return fileUpload().list()
+            .ofMinSize( 1 ).ofMaxSize( MAX_FILES )
+            .filter( us -> us.stream().mapToInt( u -> u.getBytes().remaining() ).sum() <= MAX_SIZE );
+    }
+
+    private static FileUpload file( String name, ByteBuffer buffer )
+    {
+        byte[] checksum = FileUpload.getDigest( buffer );
+        if( checksum == null ) throw new IllegalStateException( "Failed to compute checksum" );
+
+        return new FileUpload( name, buffer, checksum );
+    }
+
+    public static Matcher<FileUpload> uploadEqual( FileUpload upload )
+    {
+        return allOf(
+            contramap( equalTo( upload.getName() ), "name", FileUpload::getName ),
+            contramap( equalTo( upload.getChecksum() ), "checksum", FileUpload::getChecksum ),
+            contramap( bufferEqual( upload.getBytes() ), "bytes", FileUpload::getBytes )
+        );
+    }
+}

src/test/java/dan200/computercraft/support/ArbitraryByteBuffer.java

@@ -0,0 +1,196 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.support;
+
+import net.jqwik.api.*;
+import net.jqwik.api.arbitraries.SizableArbitrary;
+
+import javax.annotation.Nonnull;
+import javax.annotation.Nullable;
+import java.math.BigInteger;
+import java.nio.ByteBuffer;
+import java.util.Arrays;
+import java.util.Random;
+import java.util.Spliterators;
+import java.util.function.Consumer;
+import java.util.function.ToIntFunction;
+import java.util.stream.Stream;
+import java.util.stream.StreamSupport;
+
+/**
+ * Generate arbitrary byte buffers with irrelevant (but random) contents.
+ * <p>
+ * This is more efficient than using {@link Arbitraries#bytes()} and {@link Arbitrary#array(Class)}, as it does not
+ * try to shrink the contents, only the size.
+ */
+public final class ArbitraryByteBuffer implements SizableArbitrary<ByteBuffer>
+{
+    private static final ArbitraryByteBuffer DEFAULT = new ArbitraryByteBuffer( 0, null, null );
+
+    private int minSize = 0;
+    private final @Nullable Integer maxSize;
+    private final @Nullable RandomDistribution distribution;
+
+    private ArbitraryByteBuffer( int minSize, @Nullable Integer maxSize, @Nullable RandomDistribution distribution )
+    {
+        this.minSize = minSize;
+        this.maxSize = maxSize;
+        this.distribution = distribution;
+    }
+
+    public static ArbitraryByteBuffer bytes()
+    {
+        return DEFAULT;
+    }
+
+    @Nonnull
+    @Override
+    public SizableArbitrary<ByteBuffer> ofMinSize( int minSize )
+    {
+        return new ArbitraryByteBuffer( minSize, maxSize, distribution );
+    }
+
+    @Nonnull
+    @Override
+    public SizableArbitrary<ByteBuffer> ofMaxSize( int maxSize )
+    {
+        return new ArbitraryByteBuffer( minSize, maxSize, distribution );
+    }
+
+    @Nonnull
+    @Override
+    public SizableArbitrary<ByteBuffer> withSizeDistribution( @Nonnull RandomDistribution distribution )
+    {
+        return new ArbitraryByteBuffer( minSize, maxSize, distribution );
+    }
+
+    @Nonnull
+    @Override
+    public RandomGenerator<ByteBuffer> generator( int genSize )
+    {
+        BigInteger min = BigInteger.valueOf( minSize );
+        ToIntFunction<Random> generator;
+        if( distribution == null )
+        {
+            generator = sizeGeneratorWithCutoff( minSize, getMaxSize(), genSize );
+        }
+        else
+        {
+            RandomDistribution.RandomNumericGenerator gen = distribution.createGenerator( genSize, min, BigInteger.valueOf( getMaxSize() ), min );
+            generator = r -> gen.next( r ).intValueExact();
+        }
+        return r -> {
+            int size = generator.applyAsInt( r );
+            return new ShrinkableBuffer( allocateRandom( size, r ), minSize );
+        };
+    }
+
+    @Nonnull
+    @Override
+    public EdgeCases<ByteBuffer> edgeCases( int maxEdgeCases )
+    {
+        return EdgeCases.fromSuppliers( Arrays.asList(
+            () -> new ShrinkableBuffer( allocateRandom( minSize, new Random() ), minSize ),
+            () -> new ShrinkableBuffer( allocateRandom( getMaxSize(), new Random() ), minSize )
+        ) );
+    }
+
+    private int getMaxSize()
+    {
+        return maxSize == null ? Math.max( minSize * 2, 255 ) : maxSize;
+    }
+
+    private static ToIntFunction<Random> sizeGeneratorWithCutoff( int minSize, int maxSize, int genSize )
+    {
+        // If we've a large range, we either pick between generating small (<10) or large lists.
+        int range = maxSize - minSize;
+        int offset = (int) Math.max( Math.round( Math.sqrt( genSize ) ), 10 );
+        int cutoff = range <= offset ? maxSize : Math.min( offset + minSize, maxSize );
+
+        if( cutoff >= maxSize ) return random -> nextInt( random, minSize, maxSize );
+
+        // Choose size below cutoff with probability of 0.1.
+        double maxSizeProbability = Math.min( 0.02, 1.0 / (genSize / 10.0) );
+        double cutoffProbability = 0.1;
+        return random -> {
+            if( random.nextDouble() <= maxSizeProbability )
+            {
+                return maxSize;
+            }
+            else if( random.nextDouble() <= cutoffProbability + maxSizeProbability )
+            {
+                return nextInt( random, cutoff + 1, maxSize );
+            }
+            else
+            {
+                return nextInt( random, minSize, cutoff );
+            }
+        };
+    }
+
+    private static int nextInt( Random random, int minSize, int maxSize )
+    {
+        return random.nextInt( maxSize - minSize + 1 ) + minSize;
+    }
+
+    private static ByteBuffer allocateRandom( int size, Random random )
+    {
+        ByteBuffer buffer = ByteBuffer.allocate( size );
+
+        for( int i = 0; i < size; i++ ) buffer.put( i, (byte) random.nextInt() );
+        return buffer.asReadOnlyBuffer();
+    }
+
+    private static final class ShrinkableBuffer implements Shrinkable<ByteBuffer>
+    {
+        private final ByteBuffer value;
+        private final int minSize;
+
+        private ShrinkableBuffer( ByteBuffer value, int minSize )
+        {
+            this.value = value;
+            this.minSize = minSize;
+        }
+
+        @Nonnull
+        @Override
+        public ByteBuffer value()
+        {
+            return value;
+        }
+
+        @Nonnull
+        @Override
+        public Stream<Shrinkable<ByteBuffer>> shrink()
+        {
+            return StreamSupport.stream( new Spliterators.AbstractSpliterator<Shrinkable<ByteBuffer>>( 3, 0 )
+            {
+                int size = value.remaining();
+
+                @Override
+                public boolean tryAdvance( Consumer<? super Shrinkable<ByteBuffer>> action )
+                {
+                    if( size <= minSize ) return false;
+
+                    int half = (size / 2) - (minSize / 2);
+                    size = half == 0 ? minSize : size - half;
+
+                    ByteBuffer slice = value.duplicate();
+                    slice.limit( size );
+                    action.accept( new ShrinkableBuffer( slice.slice(), minSize ) );
+                    return true;
+                }
+            }, false );
+        }
+
+        @Nonnull
+        @Override
+        public ShrinkingDistance distance()
+        {
+            return ShrinkingDistance.of( value.remaining() - minSize );
+        }
+    }
+}

src/test/java/dan200/computercraft/support/ByteBufferMatcher.java

@@ -0,0 +1,75 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.support;
+
+import org.hamcrest.Description;
+import org.hamcrest.Matcher;
+import org.hamcrest.TypeSafeMatcher;
+
+import java.nio.ByteBuffer;
+
+public final class ByteBufferMatcher extends TypeSafeMatcher<ByteBuffer>
+{
+    private final ByteBuffer expected;
+
+    private ByteBufferMatcher( ByteBuffer expected )
+    {
+        this.expected = expected;
+    }
+
+    @Override
+    protected boolean matchesSafely( ByteBuffer actual )
+    {
+        return expected.equals( actual );
+    }
+
+    @Override
+    public void describeTo( Description description )
+    {
+        description.appendValue( expected );
+    }
+
+    @Override
+    protected void describeMismatchSafely( ByteBuffer actual, Description mismatchDescription )
+    {
+        if( expected.remaining() != actual.remaining() )
+        {
+            mismatchDescription
+                .appendValue( actual ).appendText( " has " ).appendValue( actual.remaining() ).appendText( " bytes remaining" );
+            return;
+        }
+
+        int remaining = expected.remaining();
+        int expectedPos = expected.position();
+        int actualPos = actual.position();
+        for( int i = 0; i < remaining; i++ )
+        {
+            if( expected.get( expectedPos + i ) == actual.get( actualPos + i ) ) continue;
+
+            int offset = Math.max( i - 5, 0 );
+            int length = Math.min( i + 5, remaining - 1 ) - offset + 1;
+
+            byte[] expectedBytes = new byte[length];
+            expected.duplicate().position( expectedPos + offset );
+            expected.get( expectedBytes );
+
+            byte[] actualBytes = new byte[length];
+            actual.duplicate().position( actualPos + offset );
+            actual.get( actualBytes );
+
+            mismatchDescription
+                .appendText( "failed at " ).appendValue( i ).appendText( System.lineSeparator() )
+                .appendText( "expected " ).appendValue( expectedBytes ).appendText( System.lineSeparator() )
+                .appendText( "was " ).appendValue( actual );
+            return;
+        }
+    }
+
+    public static Matcher<ByteBuffer> bufferEqual( ByteBuffer buffer )
+    {
+        return new ByteBufferMatcher( buffer );
+    }
+}

src/test/java/dan200/computercraft/support/CustomMatchers.java

@@ -0,0 +1,32 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.support;
+
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import static org.hamcrest.Matchers.contains;
+
+public class CustomMatchers
+{
+    /**
+     * Assert two lists are equal according to some matcher.
+     * <p>
+     * This method is simple, but helps avoid some issues with generics we'd see otherwise.
+     *
+     * @param items   The items the matched list should be equal to.
+     * @param matcher Generate a matcher for a single item in the list.
+     * @param <T>     The type to compare against.
+     * @return A matcher which compares against a list of items.
+     */
+    public static <T> Matcher<Iterable<? extends T>> containsWith( List<T> items, Function<T, Matcher<? super T>> matcher )
+    {
+        return contains( items.stream().map( matcher ).collect( Collectors.toList() ) );
+    }
+}

src/test/java/dan200/computercraft/support/CustomSampleUploadReporter.java

@@ -0,0 +1,40 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.support;
+
+import com.google.auto.service.AutoService;
+import dan200.computercraft.shared.computer.upload.FileUpload;
+import net.jqwik.api.SampleReportingFormat;
+
+import javax.annotation.Nonnull;
+
+/**
+ * Custom jqwik formatters for some of our internal types.
+ */
+@AutoService( SampleReportingFormat.class )
+public class CustomSampleUploadReporter implements SampleReportingFormat
+{
+    @Override
+    public boolean appliesTo( @Nonnull Object value )
+    {
+        return value instanceof FileUpload;
+    }
+
+    @Nonnull
+    @Override
+    public Object report( @Nonnull Object value )
+    {
+        if( value instanceof FileUpload )
+        {
+            FileUpload upload = (FileUpload) value;
+            return String.format( "FileUpload(name=%s, contents=%s)", upload.getName(), upload.getBytes() );
+        }
+        else
+        {
+            throw new IllegalStateException( "Unexpected value  " + value );
+        }
+    }
+}

src/test/java/dan200/computercraft/support/FakeContainer.java

@@ -0,0 +1,25 @@
+/*
+ * This file is part of ComputerCraft - http://www.computercraft.info
+ * Copyright Daniel Ratcliffe, 2011-2022. Do not distribute without permission.
+ * Send enquiries to dratcliffe@gmail.com
+ */
+package dan200.computercraft.support;
+
+import net.minecraft.entity.player.PlayerEntity;
+import net.minecraft.inventory.container.Container;
+
+import javax.annotation.Nonnull;
+
+public class FakeContainer extends Container
+{
+    public FakeContainer()
+    {
+        super( null, 0 );
+    }
+
+    @Override
+    public boolean stillValid( @Nonnull PlayerEntity player )
+    {
+        return true;
+    }
+}