initial commit

java/base/Asserts.java

@@ -0,0 +1,84 @@
+package base;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.Locale;
+import java.util.Objects;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+@SuppressWarnings("StaticMethodOnlyUsedInOneClass")
+public final class Asserts {
+    static {
+        Locale.setDefault(Locale.US);
+    }
+
+    private Asserts() {
+    }
+
+    public static void assertEquals(final String message, final Object expected, final Object actual) {
+        final String reason = String.format("%s:%n     expected `%s`,%n       actual `%s`",
+                message, toString(expected), toString(actual));
+        assertTrue(reason, Objects.deepEquals(expected, actual));
+    }
+
+    public static String toString(final Object value) {
+        if (value != null && value.getClass().isArray()) {
+            final String result = Arrays.deepToString(new Object[]{value});
+            return result.substring(1, result.length() - 1);
+        } else {
+            return Objects.toString(value);
+        }
+    }
+
+    public static <T> void assertEquals(final String message, final List<T> expected, final List<T> actual) {
+        for (int i = 0; i < Math.min(expected.size(), actual.size()); i++) {
+            assertEquals(message + ":" + (i + 1), expected.get(i), actual.get(i));
+        }
+        assertEquals(message + ": Number of items", expected.size(), actual.size());
+    }
+
+    public static void assertTrue(final String message, final boolean value) {
+        if (!value) {
+            throw error("%s", message);
+        }
+    }
+
+    public static void assertEquals(final String message, final double expected, final double actual, final double precision) {
+        assertTrue(
+                String.format("%s: Expected %.12f, found %.12f", message, expected, actual),
+                isEqual(expected, actual, precision)
+        );
+    }
+
+    public static boolean isEqual(final double expected, final double actual, final double precision) {
+        final double error = Math.abs(actual - expected);
+        return error <= precision
+               || error <= precision * Math.abs(expected)
+               || !Double.isFinite(expected)
+               || Math.abs(expected) > 1e100
+               || Math.abs(expected) < precision && !Double.isFinite(actual);
+    }
+
+    public static void assertSame(final String message, final Object expected, final Object actual) {
+        assertTrue(String.format("%s: expected same objects: %s and %s", message, expected, actual), expected == actual);
+    }
+
+    public static void checkAssert(final Class<?> c) {
+        if (!c.desiredAssertionStatus()) {
+            throw error("You should enable assertions by running 'java -ea %s'", c.getName());
+        }
+    }
+
+    public static AssertionError error(final String format, final Object... args) {
+        final String message = String.format(format, args);
+        return args.length > 0 && args[args.length - 1] instanceof Throwable
+               ? new AssertionError(message, (Throwable) args[args.length - 1])
+               : new AssertionError(message);
+    }
+
+    public static void printStackTrace(final String message) {
+        new Exception(message).printStackTrace(System.out);
+    }
+}

java/base/BaseChecker.java

@@ -0,0 +1,20 @@
+package base;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public abstract class BaseChecker {
+    protected final TestCounter counter;
+
+    protected BaseChecker(final TestCounter counter) {
+        this.counter = counter;
+    }
+
+    public ExtendedRandom random() {
+        return counter.random();
+    }
+
+    public int mode() {
+        return counter.mode();
+    }
+}

java/base/Either.java

@@ -0,0 +1,95 @@
+package base;
+
+import java.util.function.Function;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public interface Either<L, R> {
+    <NR> Either<L, NR> mapRight(final Function<? super R, NR> f);
+    <NR> Either<L, NR> flatMapRight(final Function<? super R, ? extends Either<L, NR>> f);
+    <T> T either(Function<? super L, ? extends T> lf, Function<? super R, ? extends T> rf);
+
+    boolean isRight();
+
+    L getLeft();
+    R getRight();
+
+    static <L, R> Either<L, R> right(final R value) {
+        return new Either<>() {
+            @Override
+            public <NR> Either<L, NR> mapRight(final Function<? super R, NR> f) {
+                return right(f.apply(value));
+            }
+
+            @Override
+            public <NR> Either<L, NR> flatMapRight(final Function<? super R, ? extends Either<L, NR>> f) {
+                return f.apply(value);
+            }
+
+            @Override
+            public <T> T either(final Function<? super L, ? extends T> lf, final Function<? super R, ? extends T> rf) {
+                return rf.apply(value);
+            }
+
+            @Override
+            public boolean isRight() {
+                return true;
+            }
+
+            @Override
+            public L getLeft() {
+                return null;
+            }
+
+            @Override
+            public R getRight() {
+                return value;
+            }
+
+            @Override
+            public String toString() {
+                return String.format("Right(%s)", value);
+            }
+        };
+    }
+
+    static <L, R> Either<L, R> left(final L value) {
+        return new Either<>() {
+            @Override
+            public <NR> Either<L, NR> mapRight(final Function<? super R, NR> f) {
+                return left(value);
+            }
+
+            @Override
+            public <NR> Either<L, NR> flatMapRight(final Function<? super R, ? extends Either<L, NR>> f) {
+                return left(value);
+            }
+
+            @Override
+            public <T> T either(final Function<? super L, ? extends T> lf, final Function<? super R, ? extends T> rf) {
+                return lf.apply(value);
+            }
+
+            @Override
+            public boolean isRight() {
+                return false;
+            }
+
+            @Override
+            public L getLeft() {
+                return value;
+            }
+
+            @Override
+            public R getRight() {
+                return null;
+            }
+
+            @Override
+            public String toString() {
+                return String.format("Left(%s)", value);
+            }
+        };
+    }
+}

java/base/ExtendedRandom.java

@@ -0,0 +1,89 @@
+package base;
+
+import java.util.Collections;
+import java.util.List;
+import java.util.Random;
+import java.util.function.Function;
+import java.util.stream.Stream;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public final class ExtendedRandom {
+    public static final String ENGLISH = "abcdefghijklmnopqrstuvwxyz";
+    public static final String RUSSIAN = "абвгдеежзийклмнопрстуфхцчшщъыьэюя";
+    public static final String GREEK = "αβγŋδεζηθικλμνξοπρτυφχψω";
+    @SuppressWarnings("StaticMethodOnlyUsedInOneClass")
+    public static final String SPACES = " \t\n\u000B\u2029\f";
+
+    private final Random random;
+
+    public ExtendedRandom(final Random random) {
+        this.random = random;
+    }
+
+    public ExtendedRandom(final Class<?> owner) {
+        this(new Random(7912736473497634913L + owner.getName().hashCode()));
+    }
+
+    public String randomString(final String chars) {
+        return randomChar(chars) + (random.nextBoolean() ? "" : randomString(chars));
+    }
+
+    public char randomChar(final String chars) {
+        return chars.charAt(nextInt(chars.length()));
+    }
+
+    public String randomString(final String chars, final int length) {
+        final StringBuilder string = new StringBuilder();
+        for (int i = 0; i < length; i++) {
+            string.append(randomChar(chars));
+        }
+        return string.toString();
+    }
+
+    public String randomString(final String chars, final int minLength, final int maxLength) {
+        return randomString(chars, nextInt(minLength, maxLength));
+    }
+
+    public boolean nextBoolean() {
+        return random.nextBoolean();
+    }
+
+    public int nextInt() {
+        return random.nextInt();
+    }
+
+    public int nextInt(final int min, final int max) {
+        return nextInt(max - min + 1) + min;
+    }
+
+    public int nextInt(final int n) {
+        return random.nextInt(n);
+    }
+
+    @SafeVarargs
+    public final <T> T randomItem(final T... items) {
+        return items[nextInt(items.length)];
+    }
+
+    public <T> T randomItem(final List<T> items) {
+        return items.get(nextInt(items.size()));
+    }
+
+    public Random getRandom() {
+        return random;
+    }
+
+    public  <T> List<T> random(final int list, final Function<ExtendedRandom, T> generator) {
+        return Stream.generate(() -> generator.apply(this)).limit(list).toList();
+    }
+
+    public double nextDouble() {
+        return random.nextDouble();
+    }
+
+    public <E> void shuffle(final List<E> all) {
+        Collections.shuffle(all, random);
+    }
+}

java/base/Functional.java

@@ -0,0 +1,92 @@
+package base;
+
+import java.util.*;
+import java.util.function.BiConsumer;
+import java.util.function.BiFunction;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+import java.util.stream.Stream;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public final class Functional {
+    private Functional() {}
+
+    public static <T, R> List<R> map(final Collection<T> items, final Function<? super T, ? extends R> f) {
+        return items.stream().map(f).collect(Collectors.toUnmodifiableList());
+    }
+
+    public static <T, R> List<R> map(final List<T> items, final BiFunction<? super Integer, ? super T, ? extends R> f) {
+        return IntStream.range(0, items.size())
+                .mapToObj(i -> f.apply(i, items.get(i)))
+                .collect(Collectors.toUnmodifiableList());
+    }
+
+    public static <K, T, R> Map<K, R> mapValues(final Map<K, T> map, final Function<T, R> f) {
+        return map.entrySet().stream().collect(Collectors.toMap(Map.Entry::getKey, e -> f.apply(e.getValue())));
+    }
+
+    @SafeVarargs
+    public static <K, T> Map<K, T> mergeMaps(final Map<K, T>... maps) {
+        return Stream.of(maps).flatMap(m -> m.entrySet().stream())
+                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue, (a, b) -> a));
+    }
+
+    @SafeVarargs
+    public static <T> List<T> concat(final Collection<? extends T>... items) {
+        final List<T> result = new ArrayList<>();
+        for (final Collection<? extends T> item : items) {
+            result.addAll(item);
+        }
+        return result;
+    }
+
+    public static <T> List<T> append(final Collection<T> collection, final T item) {
+        final List<T> list = new ArrayList<>(collection);
+        list.add(item);
+        return list;
+    }
+
+    public static <T> List<List<T>> allValues(final List<T> vals, final int length) {
+        return Stream.generate(() -> vals)
+                .limit(length)
+                .reduce(
+                        List.of(List.of()),
+                        (prev, next) -> next.stream()
+                                .flatMap(value -> prev.stream().map(list -> append(list, value)))
+                                .toList(),
+                        (prev, next) -> next.stream()
+                                .flatMap(suffix -> prev.stream().map(prefix -> concat(prefix, suffix)))
+                                .toList()
+                );
+    }
+
+    public static <K, V> V get(final Map<K, V> map, final K key) {
+        final V result = map.get(key);
+        if (result == null) {
+            throw new NullPointerException(key.toString() + " in " + map(map.keySet(), Objects::toString));
+        }
+        return result;
+    }
+
+    public static void addRange(final List<Integer> values, final int d, final int c) {
+        for (int i = -d; i <= d; i++) {
+            values.add(c + i);
+        }
+    }
+
+    public static <T> void forEachPair(final T[] items, final BiConsumer<? super T, ? super T> consumer) {
+        assert items.length % 2 == 0;
+        IntStream.range(0, items.length / 2).forEach(i -> consumer.accept(items[i * 2], items[i * 2 + 1]));
+    }
+
+
+    public static <T> List<Pair<T, T>> toPairs(final T[] items) {
+        assert items.length % 2 == 0;
+        return IntStream.range(0, items.length / 2)
+                .mapToObj(i -> Pair.of(items[i * 2], items[i * 2 + 1]))
+                .toList();
+    }
+}

java/base/Log.java

@@ -0,0 +1,56 @@
+package base;
+
+import java.util.function.Supplier;
+import java.util.regex.Pattern;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public class Log {
+    private final Pattern LINES = Pattern.compile("\n");
+    private int indent;
+
+    public static Supplier<Void> action(final Runnable action) {
+        return () -> {
+            action.run();
+            return null;
+        };
+    }
+
+    public void scope(final String name, final Runnable action) {
+        scope(name, action(action));
+    }
+
+    public <T> T scope(final String name, final Supplier<T> action) {
+        println(name);
+        indent++;
+        try {
+            return silentScope(name, action);
+        } finally {
+            indent--;
+        }
+    }
+
+    public <T> T silentScope(final String ignoredName, final Supplier<T> action) {
+        return action.get();
+    }
+
+    @SuppressWarnings("UseOfSystemOutOrSystemErr")
+    public void println(final Object value) {
+        for (final String line : LINES.split(String.valueOf(value))) {
+            System.out.println(indent() + line);
+        }
+    }
+
+    public void format(final String format, final Object... args) {
+        println(String.format(format,args));
+    }
+
+    private String indent() {
+        return "    ".repeat(indent);
+    }
+
+    protected int getIndent() {
+        return indent;
+    }
+}

java/base/MainChecker.java

@@ -0,0 +1,28 @@
+package base;
+
+import java.util.List;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+@SuppressWarnings("StaticMethodOnlyUsedInOneClass")
+public final class MainChecker {
+    private final Runner runner;
+
+    public MainChecker(final Runner runner) {
+        this.runner = runner;
+    }
+
+    public List<String> run(final TestCounter counter, final String... input) {
+        return runner.run(counter, input);
+    }
+
+    public List<String> run(final TestCounter counter, final List<String> input) {
+        return runner.run(counter, input);
+    }
+
+    public void testEquals(final TestCounter counter, final List<String> input, final List<String> expected) {
+        runner.testEquals(counter, input, expected);
+    }
+
+}

java/base/Named.java

@@ -0,0 +1,15 @@
+package base;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public record Named<T>(String name, T value) {
+    public static <T> Named<T> of(final String name, final T f) {
+        return new Named<>(name, f);
+    }
+
+    @Override
+    public String toString() {
+        return name;
+    }
+}

java/base/Pair.java

@@ -0,0 +1,44 @@
+package base;
+
+import java.util.Map;
+import java.util.function.BinaryOperator;
+import java.util.function.Function;
+import java.util.function.UnaryOperator;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+@SuppressWarnings({"StaticMethodOnlyUsedInOneClass", "unused"})
+public record Pair<F, S>(F first, S second) {
+    public static <F, S> Pair<F, S> of(final F first, final S second) {
+        return new Pair<>(first, second);
+    }
+
+    public static <F, S> Pair<F, S> of(final Map.Entry<F, S> e) {
+        return of(e.getKey(), e.getValue());
+    }
+
+    public static <F, S> UnaryOperator<Pair<F, S>> lift(final UnaryOperator<F> f, final UnaryOperator<S> s) {
+        return p -> of(f.apply(p.first), s.apply(p.second));
+    }
+
+    public static <F, S> BinaryOperator<Pair<F, S>> lift(final BinaryOperator<F> f, final BinaryOperator<S> s) {
+        return (p1, p2) -> of(f.apply(p1.first, p2.first), s.apply(p1.second, p2.second));
+    }
+
+    public static <T, F, S> Function<T, Pair<F, S>> tee(
+            final Function<? super T, ? extends F> f,
+            final Function<? super T, ? extends S> s
+    ) {
+        return t -> of(f.apply(t), s.apply(t));
+    }
+
+    @Override
+    public String toString() {
+        return "(" + first + ", " + second + ")";
+    }
+
+    public <R> Pair<F, R> second(final R second) {
+        return new Pair<>(first, second);
+    }
+}

java/base/Runner.java

@@ -0,0 +1,185 @@
+package base;
+
+import java.io.*;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.lang.reflect.Modifier;
+import java.net.MalformedURLException;
+import java.net.URL;
+import java.net.URLClassLoader;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+@SuppressWarnings("unused")
+@FunctionalInterface
+public interface Runner {
+    List<String> run(final TestCounter counter, final List<String> input);
+
+    default List<String> run(final TestCounter counter, final String... input) {
+        return run(counter, List.of(input));
+    }
+
+    default void testEquals(final TestCounter counter, final List<String> input, final List<String> expected) {
+        counter.test(() -> {
+            final List<String> actual = run(counter, input);
+            for (int i = 0; i < Math.min(expected.size(), actual.size()); i++) {
+                final String exp = expected.get(i);
+                final String act = actual.get(i);
+                if (!exp.equalsIgnoreCase(act)) {
+                    Asserts.assertEquals("Line " + (i + 1), exp, act);
+                    return;
+                }
+            }
+            Asserts.assertEquals("Number of lines", expected.size(), actual.size());
+        });
+    }
+
+    static Packages packages(final String... packages) {
+        return new Packages(List.of(packages));
+    }
+
+    @FunctionalInterface
+    interface CommentRunner {
+        List<String> run(String comment, TestCounter counter, List<String> input);
+    }
+
+    final class Packages {
+        private final List<String> packages;
+
+        private Packages(final List<String> packages) {
+            this.packages = packages;
+        }
+
+        public Runner std(final String className) {
+            final CommentRunner main = main(className);
+            return (counter, input) -> counter.call("io", () -> {
+                final ByteArrayOutputStream baos = new ByteArrayOutputStream();
+                try (final PrintWriter writer = new PrintWriter(baos, false, StandardCharsets.UTF_8)) {
+                    input.forEach(writer::println);
+                }
+
+                final InputStream oldIn = System.in;
+                try {
+                    System.setIn(new ByteArrayInputStream(baos.toByteArray()));
+                    return main.run(String.format("[%d input lines]", input.size()), counter, List.of());
+                } finally {
+                    System.setIn(oldIn);
+                }
+            });
+        }
+
+        @SuppressWarnings("ConfusingMainMethod")
+        public CommentRunner main(final String className) {
+            final Method method = findMain(className);
+
+            return (comment, counter, input) -> {
+                counter.format("Running test %02d: java %s %s%n", counter.getTestNo(), method.getDeclaringClass().getName(), comment);
+                final ByteArrayOutputStream out = new ByteArrayOutputStream();
+                @SuppressWarnings("UseOfSystemOutOrSystemErr") final PrintStream oldOut = System.out;
+                try {
+                    System.setOut(new PrintStream(out, false, StandardCharsets.UTF_8));
+                    method.invoke(null, new Object[]{input.toArray(String[]::new)});
+                    final BufferedReader reader = new BufferedReader(new InputStreamReader(new ByteArrayInputStream(out.toByteArray()), StandardCharsets.UTF_8));
+                    final List<String> result = new ArrayList<>();
+                    while (true) {
+                        final String line = reader.readLine();
+                        if (line == null) {
+                            if (result.isEmpty()) {
+                                result.add("");
+                            }
+                            return result;
+                        }
+                        result.add(line.trim());
+                    }
+                } catch (final InvocationTargetException e) {
+                    final Throwable cause = e.getCause();
+                    throw Asserts.error("main thrown exception %s: %s", cause.getClass().getSimpleName(), cause);
+                } catch (final Exception e) {
+                    throw Asserts.error("Cannot invoke main: %s: %s", e.getClass().getSimpleName(), e.getMessage());
+                } finally {
+                    System.setOut(oldOut);
+                }
+            };
+        }
+
+        private Method findMain(final String className) {
+            try {
+                final URL url = new File(".").toURI().toURL();
+                final List<String> candidates = packages.stream()
+                        .flatMap(pkg -> {
+                            final String prefix = pkg.isEmpty() ? pkg : pkg + ".";
+                            return Stream.of(prefix + className, prefix + "$" + className);
+                        })
+                        .toList();
+
+                //noinspection ClassLoaderInstantiation,resource,IOResourceOpenedButNotSafelyClosed
+                final URLClassLoader classLoader = new URLClassLoader(new URL[]{url});
+                for (final String candidate : candidates) {
+                    try {
+                        final Class<?> loaded = classLoader.loadClass(candidate);
+                        if (!Modifier.isPublic(loaded.getModifiers())) {
+                            throw Asserts.error("Class %s is not public", candidate);
+                        }
+                        final Method main = loaded.getMethod("main", String[].class);
+                        if (!Modifier.isPublic(main.getModifiers()) || !Modifier.isStatic(main.getModifiers())) {
+                            throw Asserts.error("Method main of class %s should be public and static", candidate);
+                        }
+                        return main;
+                    } catch (final ClassNotFoundException e) {
+                        // Ignore
+                    } catch (final NoSuchMethodException e) {
+                        throw Asserts.error("Could not find method main(String[]) in class %s", candidate, e);
+                    }
+                }
+                throw Asserts.error("Could not find neither of classes %s", candidates);
+            } catch (final MalformedURLException e) {
+                throw Asserts.error("Invalid path", e);
+            }
+        }
+
+        private static String getClassName(final String pkg, final String className) {
+            return pkg.isEmpty() ? className : pkg + "." + className;
+        }
+
+        public Runner args(final String className) {
+            final CommentRunner main = main(className);
+//            final AtomicReference<String> prev = new AtomicReference<>("");
+            return (counter, input) -> {
+                final int total = input.stream().mapToInt(String::length).sum() + input.size() * 3;
+                final String comment = total <= 300
+                        ? input.stream().collect(Collectors.joining("\" \"", "\"", "\""))
+                        : input.size() <= 100
+                        ? String.format("[%d arguments, sizes: %s]", input.size(), input.stream()
+                            .mapToInt(String::length)
+                            .mapToObj(String::valueOf)
+                            .collect(Collectors.joining(", ")))
+                        : String.format("[%d arguments, total size: %d]", input.size(), total);
+//                assert comment.length() <= 5 || !prev.get().equals(comment) : "Duplicate tests " + comment;
+//                prev.set(comment);
+                return main.run(comment, counter, input);
+            };
+        }
+
+        public Runner files(final String className) {
+            final Runner args = args(className);
+            return (counter, input) -> counter.call("io", () -> {
+                final Path inf = counter.getFile("in");
+                final Path ouf = counter.getFile("out");
+                Files.write(inf, input);
+                args.run(counter, List.of(inf.toString(), ouf.toString()));
+                final List<String> output = Files.readAllLines(ouf);
+                Files.delete(inf);
+                Files.delete(ouf);
+                return output;
+            });
+        }
+    }
+}

java/base/Selector.java

@@ -0,0 +1,143 @@
+package base;
+
+import java.util.*;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import java.util.function.Function;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public final class Selector {
+    private final Class<?> owner;
+    private final List<String> modes;
+    private final Set<String> variantNames = new LinkedHashSet<>();
+    private final Map<String, Consumer<TestCounter>> variants = new LinkedHashMap<>();
+
+    public Selector(final Class<?> owner, final String... modes) {
+        this.owner = owner;
+        this.modes = List.of(modes);
+    }
+
+    public Selector variant(final String name, final Consumer<TestCounter> operations) {
+        Asserts.assertTrue("Duplicate variant " + name, variants.put(name.toLowerCase(), operations) == null);
+        variantNames.add(name);
+        return this;
+    }
+
+    private static void check(final boolean condition, final String format, final Object... args) {
+        if (!condition) {
+            throw new IllegalArgumentException(String.format(format, args));
+        }
+    }
+
+    @SuppressWarnings("UseOfSystemOutOrSystemErr")
+    public void main(final String... args) {
+        try {
+            final String mode;
+            if (modes.isEmpty()) {
+                check(args.length >= 1, "At least one argument expected, found %s", args.length);
+                mode = "";
+            } else {
+                check(args.length >= 2, "At least two arguments expected, found %s", args.length);
+                mode = args[0];
+            }
+
+            final List<String> vars = Arrays.stream(args).skip(modes.isEmpty() ? 0 : 1)
+                    .flatMap(arg -> Arrays.stream(arg.split("[ +]+")))
+                    .toList();
+
+            test(mode, vars);
+        } catch (final IllegalArgumentException e) {
+            System.err.println("ERROR: " + e.getMessage());
+            if (modes.isEmpty()) {
+                System.err.println("Usage: " + owner.getName() + " VARIANT...");
+            } else {
+                System.err.println("Usage: " + owner.getName() + " MODE VARIANT...");
+                System.err.println("Modes: " + String.join(", ", modes));
+            }
+            System.err.println("Variants: " + String.join(", ", variantNames));
+            System.exit(1);
+        }
+    }
+
+    public void test(final String mode, List<String> vars) {
+        final int modeNo = modes.isEmpty() ? -1 : modes.indexOf(mode) ;
+        check(modes.isEmpty() || modeNo >= 0, "Unknown mode '%s'", mode);
+        if (variantNames.contains("Base") && !vars.contains("Base")) {
+            vars = new ArrayList<>(vars);
+            vars.add(0, "Base");
+        }
+
+        vars.forEach(variant -> check(variants.containsKey(variant.toLowerCase()), "Unknown variant '%s'", variant));
+
+        final Map<String, String> properties = modes.isEmpty()
+                                               ? Map.of("variant", String.join("+", vars))
+                                               : Map.of("variant", String.join("+", vars), "mode", mode);
+        final TestCounter counter = new TestCounter(owner, modeNo, properties);
+        counter.printHead();
+        vars.forEach(variant -> counter.scope("Testing " + variant, () -> variants.get(variant.toLowerCase()).accept(counter)));
+        counter.printStatus();
+    }
+
+    public static <V extends Tester> Composite<V> composite(final Class<?> owner, final Function<TestCounter, V> factory, final String... modes) {
+        return new Composite<>(owner, factory, (tester, counter) -> tester.test(), modes);
+    }
+
+    public static <V> Composite<V> composite(final Class<?> owner, final Function<TestCounter, V> factory, final BiConsumer<V, TestCounter> tester, final String... modes) {
+        return new Composite<>(owner, factory, tester, modes);
+    }
+
+    public List<String> getModes() {
+        return modes.isEmpty() ? List.of("~") : modes;
+    }
+
+    public List<String> getVariants() {
+        return List.copyOf(variants.keySet());
+    }
+
+    /**
+     * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+     */
+    public static final class Composite<V> {
+        private final Selector selector;
+        private final Function<TestCounter, V> factory;
+        private final BiConsumer<V, TestCounter> tester;
+        private List<Consumer<? super V>> base;
+
+        private Composite(final Class<?> owner, final Function<TestCounter, V> factory, final BiConsumer<V, TestCounter> tester, final String... modes) {
+            selector = new Selector(owner, modes);
+            this.factory = factory;
+            this.tester = tester;
+        }
+
+        @SafeVarargs
+        public final Composite<V> variant(final String name, final Consumer<? super V>... parts) {
+            if ("Base".equalsIgnoreCase(name)) {
+                base = List.of(parts);
+                return v(name.toLowerCase());
+            } else {
+                return v(name, parts);
+            }
+        }
+
+        @SafeVarargs
+        private Composite<V> v(final String name, final Consumer<? super V>... parts) {
+            selector.variant(name, counter -> {
+                final V variant = factory.apply(counter);
+                for (final Consumer<? super V> part : base) {
+                    part.accept(variant);
+                }
+                for (final Consumer<? super V> part : parts) {
+                    part.accept(variant);
+                }
+                tester.accept(variant, counter);
+            });
+            return this;
+        }
+
+        public Selector selector() {
+            return selector;
+        }
+    }
+}

java/base/TestCounter.java

@@ -0,0 +1,184 @@
+package base;
+
+import java.io.File;
+import java.io.IOException;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.Locale;
+import java.util.Map;
+import java.util.function.Consumer;
+import java.util.function.Function;
+import java.util.function.Supplier;
+import java.util.jar.JarEntry;
+import java.util.jar.JarFile;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public class TestCounter extends Log {
+    public static final int DENOMINATOR = Integer.getInteger("base.denominator", 1);
+    public static final int DENOMINATOR2 = (int) Math.round(Math.sqrt(DENOMINATOR));
+
+    private static final String JAR_EXT = ".jar";
+    private static final SimpleDateFormat DATE_FORMAT = new SimpleDateFormat("dd.MM.yyyy HH:mm:ss");
+
+    private final Class<?> owner;
+    private final int mode;
+    private final Map<String, ?> properties;
+    private final ExtendedRandom random;
+
+    private final long start = System.currentTimeMillis();
+    private int passed;
+
+    public TestCounter(final Class<?> owner, final int mode, final Map<String, ?> properties) {
+        Locale.setDefault(Locale.US);
+        Asserts.checkAssert(getClass());
+
+        this.owner = owner;
+        this.mode = mode;
+        this.properties = properties;
+        random = new ExtendedRandom(owner);
+    }
+
+    public int mode() {
+        return mode;
+    }
+
+    public int getTestNo() {
+        return passed + 1;
+    }
+
+    public void test(final Runnable action) {
+        testV(() -> {
+            action.run();
+            return null;
+        });
+    }
+
+    public <T> void testForEach(final Iterable<? extends T> items, final Consumer<? super T> action) {
+        for (final T item : items) {
+            test(() -> action.accept(item));
+        }
+    }
+
+    public <T> T testV(final Supplier<T> action) {
+        return silentScope("Test " + getTestNo(), () -> {
+            final T result = action.get();
+            passed++;
+            return result;
+        });
+    }
+
+    private String getLine() {
+        return getIndent() == 0 ? "=" : "-";
+    }
+
+    public void printHead() {
+        println("=== " + getTitle());
+    }
+
+    public void printStatus() {
+        format("%s%n%s%n", getLine().repeat(30), getTitle());
+        format("%d tests passed in %dms%n", passed, System.currentTimeMillis() - start);
+        println("Version: " + getVersion(owner));
+        println("");
+    }
+
+    private String getTitle() {
+        return String.format("%s %s", owner.getSimpleName(), properties.isEmpty() ? "" : properties);
+    }
+
+    private static String getVersion(final Class<?> clazz) {
+        try {
+            final ClassLoader cl = clazz.getClassLoader();
+            final URL url = cl.getResource(clazz.getName().replace('.', '/') + ".class");
+            if (url == null) {
+                return "(no manifest)";
+            }
+
+            final String path = url.getPath();
+            final int index = path.indexOf(JAR_EXT);
+            if (index == -1) {
+                return DATE_FORMAT.format(new Date(new File(path).lastModified()));
+            }
+
+            final String jarPath = path.substring(0, index + JAR_EXT.length());
+            try (final JarFile jarFile = new JarFile(new File(new URI(jarPath)))) {
+                final JarEntry entry = jarFile.getJarEntry("META-INF/MANIFEST.MF");
+                return DATE_FORMAT.format(new Date(entry.getTime()));
+            }
+        } catch (final IOException | URISyntaxException e) {
+            return "error: " + e;
+        }
+    }
+
+    public <T> T call(final String message, final SupplierE<T> supplier) {
+        return get(supplier).either(e -> fail(e, "%s", message), Function.identity());
+    }
+
+    public void shouldFail(final String message, @SuppressWarnings("TypeMayBeWeakened") final RunnableE action) {
+        test(() -> get(action).either(e -> null, v -> fail("%s", message)));
+    }
+
+    public <T> T fail(final String format, final Object... args) {
+        return fail(Asserts.error(format, args));
+    }
+
+    public <T> T fail(final Throwable throwable) {
+        return fail(throwable, "%s: %s", throwable.getClass().getSimpleName(), throwable.getMessage());
+    }
+
+    public <T> T fail(final Throwable throwable, final String format, final Object... args) {
+        final String message = String.format(format, args);
+        println("ERROR: " + message);
+        throw throwable instanceof Error ? (Error) throwable : new AssertionError(throwable);
+    }
+
+    public void checkTrue(final boolean condition, final String message, final Object... args) {
+        if (!condition) {
+            fail(message, args);
+        }
+    }
+
+    public static <T> Either<Exception, T> get(final SupplierE<T> supplier) {
+        return supplier.get();
+    }
+
+    public Path getFile(final String suffix) {
+        return Paths.get(String.format("test%d.%s", getTestNo(), suffix));
+    }
+
+    public ExtendedRandom random() {
+        return random;
+    }
+
+    @FunctionalInterface
+    public interface SupplierE<T> extends Supplier<Either<Exception, T>> {
+        T getE() throws Exception;
+
+        @Override
+        default Either<Exception, T> get() {
+            try {
+                return Either.right(getE());
+            } catch (final Exception e) {
+                return Either.left(e);
+            }
+        }
+    }
+
+    @FunctionalInterface
+    public interface RunnableE extends SupplierE<Void> {
+        void run() throws Exception;
+
+        @Override
+        default Void getE() throws Exception {
+            run();
+            return null;
+        }
+    }
+}

java/base/Tester.java

@@ -0,0 +1,18 @@
+package base;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public abstract class Tester extends BaseChecker {
+    protected Tester(final TestCounter counter) {
+        super(counter);
+    }
+
+    public abstract void test();
+
+    public void run(final Class<?> test, final String... args) {
+        System.out.println("=== Testing " + test.getSimpleName() + " " + String.join(" ", args));
+        test();
+        counter.printStatus();
+    }
+}

java/base/Unit.java

@@ -0,0 +1,15 @@
+package base;
+
+/**
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+public final class Unit {
+    public static final Unit INSTANCE = new Unit();
+
+    private Unit() { }
+
+    @Override
+    public String toString() {
+        return "unit";
+    }
+}

java/base/package-info.java

@@ -0,0 +1,7 @@
+/**
+ * Common homeworks test classes
+ * of <a href="https://www.kgeorgiy.info/courses/prog-intro/">Introduction to Programming</a> course.
+ *
+ * @author Georgiy Korneev (kgeorgiy@kgeorgiy.info)
+ */
+package base;