Filtering the generating values

src/main/java/net/andreinc/mockneat/abstraction/MockUnit.java

@@ -179,6 +179,46 @@ default <R> MockUnit<R> map(Function<T, R> function) {
         return () -> supp;
     }
 
+    /**
+     * <p>Returns a generator consisting of the elements of this generator that match the given predicate.</p>
+     *
+     * @param predicate The {@code Predicate<T>} applied to the generated value in the intermediary step to determine if it should be returned.
+     * @return A new MockUnit
+     */
+    default MockUnit<T> filter(Predicate<? super T> predicate) {
+        notNull(predicate, "predicate");
+        Supplier<T> supp = () -> {
+            T val = val();
+            while (!predicate.test(val)) {
+                val = val();
+            }
+            return val;
+        };
+        return () -> supp;
+    }
+
+    /**
+     * <p>Returns a generator consisting of the distinct elements (according to {@link Object#equals(Object)}) of this generator.</p>
+     *
+     * @param function The {@code Function<T,R>} applied to the generated value for check for unique.
+     * @param <K> The type of the values for check for unique.
+     * @return A new MockUnit
+     */
+    default <K> MockUnit<T> distinctBy(Function<? super T, ? extends K> function) {
+        notNull(function, "function");
+        Set<K> seen = new HashSet<>();
+        return filter(it -> seen.add(function.apply(it)));
+    }
+
+    /**
+     * <p>Returns a generator consisting of the distinct elements (according to {@link Object#equals(Object)}) of this generator.</p>
+     *
+     * @return A new MockUnit
+     */
+    default MockUnit<T> distinct() {
+        return distinctBy(Function.identity());
+    }
+
     /**
      * <p>This method is used to transform a {@code MockUnit} into a {@code MockUnitInt}.</p>
      *

src/test/java/net/andreinc/mockneat/abstraction/MockUnitFilterMethodTest.java

@@ -0,0 +1,39 @@
+package net.andreinc.mockneat.abstraction;
+
+import org.junit.Test;
+
+import static net.andreinc.mockneat.Constants.*;
+import static net.andreinc.mockneat.utils.LoopsUtils.loop;
+import static org.junit.Assert.assertEquals;
+
+public class MockUnitFilterMethodTest {
+
+    @Test(expected = NullPointerException.class)
+    public void testFilterNullFunc() {
+        M.ints().filter(null);
+    }
+
+    @Test(expected = NullPointerException.class)
+    public void testDistinctByNullFunc() {
+        M.ints().distinctBy(null);
+    }
+
+    @Test
+    public void testFilterEven() {
+        loop(MOCK_CYCLES,
+                MOCKS,
+                m -> m.ints().filter(it -> it % 2 == 0).val(),
+                v -> assertEquals(0, v % 2)
+        );
+    }
+
+    @Test
+    public void testDistinct() {
+        loop(MOCK_CYCLES,
+                MOCKS,
+                m -> m.ints().rangeClosed(1, 10).distinct().set(10).val(),
+                v -> assertEquals(10, v.size())
+        );
+    }
+
+}