Add additional Entity constructors (cedar-policy#288)

Signed-off-by: John Brain <jnbrain@amazon.com>
Co-authored-by: Craig Disselkoen <craigdissel@gmail.com>

Author: jtbrain

CedarJava/src/main/java/com/cedarpolicy/model/entity/Entity.java

@@ -40,6 +40,25 @@ public class Entity {
     /** Tags on this entity (RFC 82) */
     public final Map<String, Value> tags;
 
+    /**
+     * Create an entity from an EntityUID. It will have no attributes, parents, or tags.
+     *
+     * @param uid EUID of the Entity.
+     */
+    public Entity(EntityUID uid) {
+        this(uid, new HashMap<>(), new HashSet<>(), new HashMap<>());
+    }
+
+    /**
+     * Create an entity from an EntityUID and a set of parent EntityUIDs. It will have no attributes or tags.
+     *
+     * @param uid EUID of the Entity.
+     * @param parentsEUIDs Set of parent entities' EUIDs.
+     */
+    public Entity(EntityUID uid, Set<EntityUID> parentsEUIDs) {
+        this(uid, new HashMap<>(), parentsEUIDs, new HashMap<>());
+    }
+
     /**
      * Create an entity from an EntityUIDs, a map of attributes, and a set of parent EntityUIDs.
      *

CedarJava/src/test/java/com/cedarpolicy/EntityTests.java

@@ -14,7 +14,7 @@
  * limitations under the License.
  */
 
- package com.cedarpolicy;
+package com.cedarpolicy;
 
 import org.junit.jupiter.api.Test;
 import static org.junit.jupiter.api.Assertions.assertThrows;
@@ -27,7 +27,6 @@
 import com.cedarpolicy.value.*;
 import com.cedarpolicy.model.entity.Entity;
 
-
 public class EntityTests {
 
     @Test
@@ -49,4 +48,37 @@ public void getAttrTests() {
         // Test key not found
         assertEquals(principal.getAttr("decimalAttr"), null);
     }
+
+    @Test
+    public void newWithEntityUIDTests() {
+        EntityTypeName principalType = EntityTypeName.parse("User").get();
+        Entity principal = new Entity(principalType.of("Alice"));
+
+        // Test the Entity's uid
+        assertEquals(principal.getEUID(), principalType.of("Alice"));
+
+        // Test that a key is not found
+        assertEquals(principal.getAttr("stringAttr"), null);
+
+        // Test the Entity's parents
+        assertEquals(principal.getParents().size(), 0);
+    }
+
+    @Test
+    public void newWithoutAttributesTests() {
+        EntityTypeName principalType = EntityTypeName.parse("User").get();
+        HashSet<EntityUID> parents = new HashSet<EntityUID>();
+        parents.add(principalType.of("Bob"));
+
+        Entity principal = new Entity(principalType.of("Alice"), parents);
+
+        // Test the Entity's uid
+        assertEquals(principal.getEUID(), principalType.of("Alice"));
+
+        // Test that a key is not found
+        assertEquals(principal.getAttr("stringAttr"), null);
+
+        // Test the Entity's parents
+        assertEquals(principal.getParents(), parents);
+    }
 }