test: add test

lang/src/main/java/com/qwlabs/lang/RuntimeExpiringMemoizingSupplier.java

@@ -2,13 +2,10 @@
 
 import com.google.common.base.Supplier;
 
-import javax.annotation.CheckForNull;
-
 public class RuntimeExpiringMemoizingSupplier<T> implements Supplier<T> {
     private final Supplier<WithExpiring<T>> delegate;
-    @CheckForNull
-    private transient volatile T value;
-    private transient volatile long expirationNanos;
+    private T value;
+    private volatile long expirationNanos;
 
     public RuntimeExpiringMemoizingSupplier(Supplier<WithExpiring<T>> delegate) {
         this.delegate = delegate;
@@ -24,7 +21,7 @@ public T get() {
             }
         }
         long now = System.nanoTime();
-        if (now > expirationNanos) {
+        if (now < expirationNanos) {
             return this.value;
         }
         synchronized (this) {

lang/src/test/java/com/qwlabs/lang/RuntimeExpiringMemoizingSupplierTest.java

@@ -0,0 +1,40 @@
+package com.qwlabs.lang;
+
+import com.google.common.base.Supplier;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+
+import java.util.concurrent.TimeUnit;
+
+import static org.hamcrest.MatcherAssert.assertThat;
+import static org.hamcrest.Matchers.is;
+import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+@ExtendWith(MockitoExtension.class)
+class RuntimeExpiringMemoizingSupplierTest {
+    @Test
+    void should_call_once(@Mock RealSupplier delegate) {
+        RuntimeExpiringMemoizingSupplier<String> supplier = new RuntimeExpiringMemoizingSupplier<>(delegate);
+
+        when(delegate.get()).thenReturn(WithExpiring.of("1", 1, TimeUnit.DAYS));
+
+        var value1 = supplier.get();
+        var value2 = supplier.get();
+
+        assertSame(value1, value2);
+        assertThat(value1, is("1"));
+
+        verify(delegate).get();
+    }
+
+    static class RealSupplier implements Supplier<WithExpiring<String>> {
+        @Override
+        public WithExpiring<String> get() {
+            return WithExpiring.of("real", 1, TimeUnit.DAYS);
+        }
+    }
+}