Merge pull request #1879 from davvd/fix-1858-equals-hashcode

#1858: fix asymmetric equals in collection.Immutable

Author: yegor256

src/main/java/org/cactoos/collection/Immutable.java

@@ -120,6 +120,8 @@ public int hashCode() {
 
     @Override
     public boolean equals(final Object obj) {
-        return this.col.equals(obj);
+        return this == obj
+            || obj instanceof Immutable
+            && this.col.equals(((Immutable<?>) obj).col);
     }
 }

src/test/java/org/cactoos/collection/ImmutableTest.java

@@ -4,6 +4,7 @@
  */
 package org.cactoos.collection;
 
+import java.util.Collection;
 import java.util.List;
 import org.cactoos.list.ListOf;
 import org.hamcrest.MatcherAssert;
@@ -234,4 +235,17 @@ void testEquals() {
             )
         );
     }
+
+    @Test
+    void equalsIsSymmetricWithPlainList() {
+        final List<Integer> plain = new ListOf<>(1, 2, 3);
+        final Collection<Integer> wrapper = new Immutable<>(
+            new ListOf<>(1, 2, 3)
+        );
+        MatcherAssert.assertThat(
+            "equals() must be symmetric between wrapper and plain list",
+            wrapper.equals(plain),
+            new IsEqual<>(plain.equals(wrapper))
+        );
+    }
 }