Move Graphs.selfLoopPredicate() to GraphsTest.java

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=124271785

guava-tests/test/com/google/common/graph/GraphsTest.java

@@ -16,12 +16,12 @@
 
 package com.google.common.graph;
 
+import static com.google.common.base.Preconditions.checkNotNull;
 import static com.google.common.graph.Graphs.addEdge;
 import static com.google.common.graph.Graphs.copyOf;
 import static com.google.common.graph.Graphs.mergeEdgesFrom;
 import static com.google.common.graph.Graphs.mergeNodesFrom;
 import static com.google.common.graph.Graphs.oppositeNode;
-import static com.google.common.graph.Graphs.selfLoopPredicate;
 import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.fail;
 
@@ -71,6 +71,22 @@ public class GraphsTest {
       "Should not be allowed to add a self-loop edge.";
   static final String ERROR_SELF_LOOP = "self-loops are not allowed";
 
+  /**
+   * Returns a {@link Predicate} that returns {@code true} if the input edge is a self-loop in
+   * {@code graph}. A self-loop is defined as an edge whose set of incident nodes has exactly one
+   * element. The predicate's {@code apply} method will throw an {@link IllegalArgumentException} if
+   * {@code graph} does not contain {@code edge}.
+   */
+  private static <E> Predicate<E> selfLoopPredicate(final Network<?, E> graph) {
+    checkNotNull(graph, "graph");
+    return new Predicate<E>() {
+      @Override
+      public boolean apply(E edge) {
+        return (graph.incidentNodes(edge).size() == 1);
+      }
+    };
+  }
+
   @Test
   public void oppositeNode_basic() {
     List<MutableNetwork<Integer, String>> testNetworks = ImmutableList.of(

guava/src/com/google/common/graph/Graphs.java

@@ -375,22 +375,6 @@ public static String toString(Network<?, ?> graph) {
         Maps.asMap(graph.edges(), edgeToIncidentNodesString(graph)));
   }
 
-  /**
-   * Returns a {@link Predicate} that returns {@code true} if the input edge is a self-loop in
-   * {@code graph}. A self-loop is defined as an edge whose set of incident nodes has exactly one
-   * element. The predicate's {@code apply} method will throw an {@link IllegalArgumentException} if
-   * {@code graph} does not contain {@code edge}.
-   */
-  public static <E> Predicate<E> selfLoopPredicate(final Network<?, E> graph) {
-    checkNotNull(graph, "graph");
-    return new Predicate<E>() {
-      @Override
-      public boolean apply(E edge) {
-        return (graph.incidentNodes(edge).size() == 1);
-      }
-    };
-  }
-
   /**
    * Returns a String of the adjacent node relationships for {@code graph}.
    */