gh-2625: Improve assertions readability with assertJ (#3014)

* gh-2625: Improve assertions readability with assertJ

* Further examples of changes for gh-2625

* Fix changes merged in from develop branch

* Copyright Header Update

---------

Co-authored-by: GCHQDeveloper314 <94527357+GCHQDeveloper314@users.noreply.github.com>
Co-authored-by: t92549 <80890692+t92549@users.noreply.github.com>

core/common-util/src/test/java/uk/gov/gchq/gaffer/commonutil/iterable/CachingIterableTest.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2018-2021 Crown Copyright
+ * Copyright 2018-2023 Crown Copyright
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -28,7 +28,6 @@
 import java.io.Closeable;
 import java.io.IOException;
 import java.util.Arrays;
-import java.util.Collections;
 import java.util.Iterator;
 import java.util.List;
 
@@ -51,8 +50,9 @@ public void shouldCacheSmallIterable(@Mock final Iterable<Integer> mockIterable)
 
         final Iterable<Integer> cachingIterable = new CachingIterable<>(mockIterable, 5);
 
-        assertThat(SMALL_LIST).isEqualTo(Lists.newArrayList(cachingIterable));
-        assertThat(SMALL_LIST).isEqualTo(Lists.newArrayList(cachingIterable));
+        assertThat(cachingIterable)
+                .containsExactlyElementsOf(SMALL_LIST)
+                .containsExactlyElementsOf(SMALL_LIST);
         verify(mockIterable, times(1)).iterator();
     }
 
@@ -64,17 +64,17 @@ public void shouldNotCacheALargeIterable(@Mock final Iterable<Integer> mockItera
 
         final Iterable<Integer> cachingIterable = new CachingIterable<>(mockIterable, 5);
 
-        assertThat(LARGE_LIST).isEqualTo(Lists.newArrayList(cachingIterable));
-        assertThat(LARGE_LIST).isEqualTo(Lists.newArrayList(cachingIterable));
+        assertThat(cachingIterable)
+                .containsExactlyElementsOf(LARGE_LIST)
+                .containsExactlyElementsOf(LARGE_LIST);
         verify(mockIterable, times(2)).iterator();
     }
 
     @Test
     public void shouldHandleNullIterable() {
         Iterable<Integer> cachingIterable = new CachingIterable<>(null);
 
-        assertThat(Collections.emptyList()).isEqualTo(Lists.newArrayList(cachingIterable));
-        assertThat(Collections.emptyList()).isEqualTo(Lists.newArrayList(cachingIterable));
+        assertThat(cachingIterable).isEmpty();
     }
 
     @Test
@@ -98,7 +98,7 @@ public void shouldCloseTheIterableWhenFullyCached() throws IOException {
 
         final Iterable<Integer> cachingIterable = new CachingIterable<>(iterable, 5);
 
-        assertThat(SMALL_LIST).isEqualTo(Lists.newArrayList(cachingIterable));
+        assertThat(cachingIterable).containsExactlyElementsOf(SMALL_LIST);
         verify((Closeable) iterable).close();
     }
 
@@ -130,15 +130,15 @@ public void shouldHandleMultipleIterators() throws IOException {
         itr3.next();
 
         final Iterator<Integer> itr4 = cachingIterable.iterator();
-        assertThat(SMALL_LIST).isEqualTo(Lists.newArrayList(itr4));
+        assertThat(Lists.newArrayList(itr4)).containsExactlyElementsOf(SMALL_LIST);
 
         // should be cached now as it has been fully read.
         verify((Closeable) iterable, times(3)).close();
 
         itr3.next();
 
         verify(iterable, times(4)).iterator();
-        assertThat(SMALL_LIST).isEqualTo(Lists.newArrayList(cachingIterable));
+        assertThat(cachingIterable).containsExactlyElementsOf(SMALL_LIST);
 
         final Iterator<Integer> itr5 = cachingIterable.iterator();
         assertThat(itr5.next()).isEqualTo((Integer) 0);