test/jdk/java/lang/StableValue/StableSupplierTest.java

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/* @test
 * @summary Basic tests for StableSupplier methods
 * @enablePreview
 * @run junit StableSupplierTest
 */

import org.junit.jupiter.api.Test;

import java.util.Objects;
import java.util.concurrent.atomic.AtomicReference;
import java.util.function.Supplier;

import static org.junit.jupiter.api.Assertions.*;

final class StableSupplierTest {

    private static final Supplier<Integer> SUPPLIER = () -> 42;

    @Test
    void factoryInvariants() {
        assertThrows(NullPointerException.class, () -> StableValue.supplier(null));
    }

    @Test
    void basic() {
        basic(SUPPLIER);
        basic(() -> null);
    }

    void basic(Supplier<Integer> supplier) {
        StableTestUtil.CountingSupplier<Integer> cs = new StableTestUtil.CountingSupplier<>(supplier);
        var cached = StableValue.supplier(cs);
        assertEquals(".unset", cached.toString());
        assertEquals(supplier.get(), cached.get());
        assertEquals(1, cs.cnt());
        assertEquals(supplier.get(), cached.get());
        assertEquals(1, cs.cnt());
        assertEquals(Objects.toString(supplier.get()), cached.toString());
    }

    @Test
    void exception() {
        StableTestUtil.CountingSupplier<Integer> cs = new StableTestUtil.CountingSupplier<>(() -> {
            throw new UnsupportedOperationException();
        });
        var cached = StableValue.supplier(cs);
        assertThrows(UnsupportedOperationException.class, cached::get);
        assertEquals(1, cs.cnt());
        assertThrows(UnsupportedOperationException.class, cached::get);
        assertEquals(2, cs.cnt());
        assertEquals(".unset", cached.toString());
    }

    @Test
    void circular() {
        final AtomicReference<Supplier<?>> ref = new AtomicReference<>();
        Supplier<Supplier<?>> cached = StableValue.supplier(ref::get);
        ref.set(cached);
        cached.get();
        String toString = cached.toString();
        assertTrue(toString.startsWith("(this StableSupplier)"));
        assertDoesNotThrow(cached::hashCode);
    }

    @Test
    void equality() {
        Supplier<Integer> f0 = StableValue.supplier(SUPPLIER);
        Supplier<Integer> f1 = StableValue.supplier(SUPPLIER);
        // No function is equal to another function
        assertNotEquals(f0, f1);
    }

    @Test
    void hashCodeStable() {
        Supplier<Integer> f0 = StableValue.supplier(SUPPLIER);
        assertEquals(System.identityHashCode(f0), f0.hashCode());
        f0.get();
        assertEquals(System.identityHashCode(f0), f0.hashCode());
    }

}