Add IdentityRandomSampling class for testing

src/main/java/gr/james/sampling/IdentityRandomSampling.java

@@ -0,0 +1,87 @@
+package gr.james.sampling;
+
+import java.util.*;
+
+/**
+ * A {@link RandomSampling} decorator that doesn't permit duplicate items.
+ *
+ * @param <T>  the element type
+ * @param <RS> the {@link RandomSampling} implementation type
+ */
+@Deprecated
+class IdentityRandomSampling<T, RS extends RandomSampling<T>> implements RandomSampling<T> {
+    private RS source;
+    private Set<T> set;
+
+    /**
+     * Decorates {@code source} as an {@link IdentityRandomSampling}.
+     * <p>
+     * The caller must ensure that {@code source} will not be accessed directly after this point.
+     *
+     * @param source the source {@link RandomSampling} implementation
+     * @throws NullPointerException     if {@code source} is {@code null}
+     * @throws IllegalArgumentException if {@code source} already had some items feeded
+     */
+    IdentityRandomSampling(RS source) {
+        if (source == null) {
+            throw new NullPointerException();
+        }
+        if (source.sample().size() != 0) {
+            throw new IllegalArgumentException();
+        }
+        this.source = source;
+        this.set = new HashSet<>();
+    }
+
+    @Override
+    public RS feed(T item) {
+        if (item == null) {
+            throw new NullPointerException();
+        }
+        if (!set.add(item)) {
+            throw new UnsupportedOperationException();
+        }
+        source.feed(item);
+        return source;
+    }
+
+    @Override
+    public RS feed(Iterator<T> items) {
+        source.feed(items);
+        return source;
+    }
+
+    @Override
+    public RS feed(Iterable<T> items) {
+        source.feed(items);
+        return source;
+    }
+
+    @Override
+    public int sampleSize() {
+        return source.sampleSize();
+    }
+
+    @Override
+    public long streamSize() {
+        return source.streamSize();
+    }
+
+    @Override
+    public Set<T> sample() {
+        assert source.sample().stream().distinct().count() == source.sample().stream().distinct().count();
+        return new AbstractSet<T>() {
+            final Collection<T> sample = source.sample();
+
+            @Override
+            public Iterator<T> iterator() {
+                return sample.iterator();
+            }
+
+            @Override
+            public int size() {
+                return sample.size();
+            }
+        };
+    }
+}