server/container/util/src/test/java/org/apache/james/util/MemoizedSupplierTest.java

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package org.apache.james.util;

import static org.assertj.core.api.Assertions.assertThat;

import java.time.Duration;
import java.util.concurrent.atomic.AtomicBoolean;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.james.util.concurrency.ConcurrentTestRunner;
import org.junit.jupiter.api.Test;

class MemoizedSupplierTest {

    @Test
    void getShouldReturnSuppliedValue() {
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> 42);

        assertThat(supplier.get()).isEqualTo(42);
    }

    @Test
    void getShouldBeIdempotent() {
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> 42);

        supplier.get();
        assertThat(supplier.get()).isEqualTo(42);
    }


    @Test
    void getShouldReturnSameMemorizedInstanceInParallel() throws Exception {
        AtomicInteger counter = new AtomicInteger(0);
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(counter::incrementAndGet);

        ConcurrentTestRunner.builder()
            .operation((threadNumber, operationNumber) -> supplier.get())
            .threadCount(20)
            .operationCount(10)
            .runSuccessfullyWithin(Duration.ofMinutes(1));

        assertThat(counter.get()).isEqualTo(1);
    }

    @Test
    void nullValueShouldBeSupported() {
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> null);

        supplier.get();
        assertThat(supplier.get()).isNull();
    }

    @Test
    void underlyingSupplierShouldBeCalledOnlyOnce() {
        AtomicInteger atomicInteger = new AtomicInteger(0);

        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> {
            atomicInteger.incrementAndGet();
            return 42;
        });

        supplier.get();
        supplier.get();

        assertThat(atomicInteger.get()).isEqualTo(1);
    }

    @Test
    void underlyingSupplierShouldBeCalledOnlyOnceWhenReturningNullValue() {
        AtomicInteger atomicInteger = new AtomicInteger(0);

        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> {
            atomicInteger.incrementAndGet();
            return null;
        });

        supplier.get();
        supplier.get();

        assertThat(atomicInteger.get()).isEqualTo(1);
    }

    @Test
    void ifInitializedShouldPerformWhenValueIsInitialized() {
        AtomicBoolean performAfterInitialization = new AtomicBoolean(false);
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> 10);

        supplier.get();
        supplier.ifInitialized(value -> performAfterInitialization.set(true));
        assertThat(performAfterInitialization.get()).isTrue();
    }

    @Test
    void ifInitializedShouldPerformOnlyOnceWhenValueIsInitializedInParallel() throws Exception {
        AtomicInteger performAfterInitializationCounter = new AtomicInteger(0);
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> 10);

        ConcurrentTestRunner.builder()
            .operation((threadNumber, operationNumber) -> supplier.get())
            .threadCount(20)
            .operationCount(10)
            .runSuccessfullyWithin(Duration.ofMinutes(1));
        supplier.ifInitialized(value -> performAfterInitializationCounter.incrementAndGet());

        assertThat(performAfterInitializationCounter.get()).isEqualTo(1);
    }


    @Test
    void ifInitializedShouldNotPerformWhenValueIsNotInitialized() {
        AtomicBoolean performAfterInitialization = new AtomicBoolean(false);
        MemoizedSupplier<Integer> supplier = MemoizedSupplier.of(() -> 10);

        supplier.ifInitialized(value -> performAfterInitialization.set(true));
        assertThat(performAfterInitialization.get()).isFalse();
    }
}