Make LazyExpression memoization disable-able

src/main/java/com/hubspot/jinjava/interpret/LazyExpression.java

@@ -6,20 +6,35 @@
 public class LazyExpression implements Supplier {
   private final Supplier supplier;
   private final String image;
+  private final Memoization memoization;
   private Object jsonValue = null;
 
-  private LazyExpression(Supplier supplier, String image) {
+  public enum Memoization {
+    ON,
+    OFF
+  }
+
+  private LazyExpression(Supplier supplier, String image, Memoization memoization) {
     this.supplier = supplier;
     this.image = image;
+    this.memoization = memoization;
   }
 
   public static LazyExpression of(Supplier supplier, String image) {
-    return new LazyExpression(supplier, image);
+    return new LazyExpression(supplier, image, Memoization.ON);
+  }
+
+  public static LazyExpression of(
+    Supplier supplier,
+    String image,
+    Memoization memoization
+  ) {
+    return new LazyExpression(supplier, image, memoization);
   }
 
   @Override
   public Object get() {
-    if (jsonValue == null) {
+    if (jsonValue == null || memoization == Memoization.OFF) {
       jsonValue = supplier.get();
     }
     return jsonValue;

src/test/java/com/hubspot/jinjava/interpret/LazyExpressionTest.java

@@ -1,10 +1,13 @@
 package com.hubspot.jinjava.interpret;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.*;
 
 import com.fasterxml.jackson.core.JsonProcessingException;
 import com.fasterxml.jackson.databind.ObjectMapper;
 import com.google.common.collect.ImmutableMap;
+import com.hubspot.jinjava.interpret.LazyExpression.Memoization;
+import java.util.List;
 import org.junit.Test;
 
 public class LazyExpressionTest {
@@ -29,4 +32,31 @@ public void itSerializesNonEvaluatedValueToEmpty() throws JsonProcessingExceptio
     );
     assertThat(new ObjectMapper().writeValueAsString(expression)).isEqualTo("\"\"");
   }
+
+  @Test
+  public void itMemoizesByDefault() {
+    List mock = mock(List.class);
+    LazyExpression expression = LazyExpression.of(mock::isEmpty, "");
+    expression.get();
+    expression.get();
+    verify(mock, times(1)).isEmpty();
+  }
+
+  @Test
+  public void itAllowsMemoizationToBeDisabled() {
+    List mock = mock(List.class);
+    LazyExpression expression = LazyExpression.of(mock::isEmpty, "", Memoization.OFF);
+    expression.get();
+    expression.get();
+    verify(mock, times(2)).isEmpty();
+  }
+
+  @Test
+  public void itAllowsMemoizationToBeEnabled() {
+    List mock = mock(List.class);
+    LazyExpression expression = LazyExpression.of(mock::isEmpty, "", Memoization.ON);
+    expression.get();
+    expression.get();
+    verify(mock, times(1)).isEmpty();
+  }
 }