Jul 18, 2025 · Jul 18, 2025 · Jul 18, 2025 · Jul 18, 2025
diff --git a/src/test/java/com/thealgorithms/datastructures/lists/SkipListTest.java b/src/test/java/com/thealgorithms/datastructures/lists/SkipListTest.java
 package com.thealgorithms.datastructures.lists;

 import static org.junit.jupiter.api.Assertions.assertArrayEquals;
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;

 import java.util.Arrays;
 import java.util.stream.IntStream;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;

 class SkipListTest {

    private SkipList<String> skipList;

    @BeforeEach
    void setUp() {
        skipList = new SkipList<>();
    }

    @Test
 void add() {
    SkipList<String> skipList = new SkipList<>();
 @DisplayName("Add element and verify size and retrieval")
 void testAdd() {
        assertEquals(0, skipList.size());

        skipList.add("value");

        print(skipList);
        assertEquals(1, skipList.size());
        assertEquals("value", skipList.get(0));
    }

    @Test
 void get() {
    SkipList<String> skipList = new SkipList<>();
 @DisplayName("Get retrieves correct element by index")
 void testGet() {
        skipList.add("value");

        String actualValue = skipList.get(0);

        print(skipList);
        assertEquals("value", actualValue);
        assertEquals("value", skipList.get(0));
    }

    @Test
    void contains() {
        SkipList<String> skipList = createSkipList();
        print(skipList);

        boolean contains = skipList.contains("b");

        assertTrue(contains);
    @DisplayName("Contains returns true if element exists")
    void testContains() {
        skipList = createSkipList();
        assertTrue(skipList.contains("b"));
        assertTrue(skipList.contains("a"));
        assertFalse(skipList.contains("z")); // negative test
    }

    @Test
    void removeFromHead() {
        SkipList<String> skipList = createSkipList();
        String mostLeftElement = skipList.get(0);
    @DisplayName("Remove element from head and check size and order")
    void testRemoveFromHead() {
        skipList = createSkipList();
        String first = skipList.get(0);
        int initialSize = skipList.size();
        print(skipList);

        skipList.remove(mostLeftElement);
        skipList.remove(first);

        print(skipList);
        assertEquals(initialSize - 1, skipList.size());
        assertFalse(skipList.contains(first));
    }

    @Test
    void removeFromTail() {
        SkipList<String> skipList = createSkipList();
        String mostRightValue = skipList.get(skipList.size() - 1);
    @DisplayName("Remove element from tail and check size and order")
    void testRemoveFromTail() {
        skipList = createSkipList();
        String last = skipList.get(skipList.size() - 1);
        int initialSize = skipList.size();
        print(skipList);

        skipList.remove(mostRightValue);
        skipList.remove(last);

        print(skipList);
        assertEquals(initialSize - 1, skipList.size());
        assertFalse(skipList.contains(last));
    }

    @Test
 void checkSortedOnLowestLayer() {
    SkipList<String> skipList = new SkipList<>();
 @DisplayName("Elements should be sorted at base level")
 void testSortedOrderOnBaseLevel() {
        String[] values = {"d", "b", "a", "c"};
        Arrays.stream(values).forEach(skipList::add);
        print(skipList);

        String[] actualOrder = IntStream.range(0, values.length).mapToObj(skipList::get).toArray(String[] ::new);

        assertArrayEquals(new String[] {"a", "b", "c", "d"}, actualOrder);
 org.junit.jupiter.api.Assertions.assertArrayEquals(new String[] {"a", "b", "c", "d"}, actualOrder);
    }

    private SkipList<String> createSkipList() {
        SkipList<String> skipList = new SkipList<>();
        String[] values = {
            "a",
            "b",
            "c",
            "d",
            "e",
            "f",
            "g",
            "h",
            "i",
            "j",
            "k",
        };
    @Test
    @DisplayName("Duplicate elements can be added and count correctly")
    void testAddDuplicates() {
        skipList.add("x");
        skipList.add("x");
        assertEquals(2, skipList.size());
        assertEquals("x", skipList.get(0));
        assertEquals("x", skipList.get(1));
    }

    @Test
    @DisplayName("Add multiple and remove all")
    void testClearViaRemovals() {
        String[] values = {"a", "b", "c"};
        Arrays.stream(values).forEach(skipList::add);
        return skipList;

        for (String v : values) {
            skipList.remove(v);
        }

        assertEquals(0, skipList.size());
    }

    /**
     * Print Skip List representation to console.
     * Optional method not involved in testing process. Used only for visualisation purposes.
     * @param skipList to print
     */
    private void print(SkipList<?> skipList) {
        System.out.println(skipList);
    private SkipList<String> createSkipList() {
        SkipList<String> s = new SkipList<>();
        String[] values = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"};
        Arrays.stream(values).forEach(s::add);
        return s;
    }
 }
Original file line number	Diff line number	Diff line change
		@@ -1,110 +1,115 @@
		package com.thealgorithms.datastructures.lists;

		import static org.junit.jupiter.api.Assertions.assertArrayEquals;
		import static org.junit.jupiter.api.Assertions.assertEquals;
		import static org.junit.jupiter.api.Assertions.assertFalse;
		import static org.junit.jupiter.api.Assertions.assertTrue;

		import java.util.Arrays;
		import java.util.stream.IntStream;
		import org.junit.jupiter.api.BeforeEach;
		import org.junit.jupiter.api.DisplayName;
		import org.junit.jupiter.api.Test;

		class SkipListTest {

		private SkipList<String> skipList;

		@BeforeEach
		void setUp() {
		skipList = new SkipList<>();
		}

		@Test
		void add() {
		SkipList<String> skipList = new SkipList<>();
		@DisplayName("Add element and verify size and retrieval")
		void testAdd() {
		assertEquals(0, skipList.size());

		skipList.add("value");

		print(skipList);
		assertEquals(1, skipList.size());
		assertEquals("value", skipList.get(0));
		}

		@Test
		void get() {
		SkipList<String> skipList = new SkipList<>();
		@DisplayName("Get retrieves correct element by index")
		void testGet() {
		skipList.add("value");

		String actualValue = skipList.get(0);

		print(skipList);
		assertEquals("value", actualValue);
		assertEquals("value", skipList.get(0));
		}

		@Test
		void contains() {
		SkipList<String> skipList = createSkipList();
		print(skipList);

		boolean contains = skipList.contains("b");

		assertTrue(contains);
		@DisplayName("Contains returns true if element exists")
		void testContains() {
		skipList = createSkipList();
		assertTrue(skipList.contains("b"));
		assertTrue(skipList.contains("a"));
		assertFalse(skipList.contains("z")); // negative test
		}

		@Test
		void removeFromHead() {
		SkipList<String> skipList = createSkipList();
		String mostLeftElement = skipList.get(0);
		@DisplayName("Remove element from head and check size and order")
		void testRemoveFromHead() {
		skipList = createSkipList();
		String first = skipList.get(0);
		int initialSize = skipList.size();
		print(skipList);

		skipList.remove(mostLeftElement);
		skipList.remove(first);

		print(skipList);
		assertEquals(initialSize - 1, skipList.size());
		assertFalse(skipList.contains(first));
		}

		@Test
		void removeFromTail() {
		SkipList<String> skipList = createSkipList();
		String mostRightValue = skipList.get(skipList.size() - 1);
		@DisplayName("Remove element from tail and check size and order")
		void testRemoveFromTail() {
		skipList = createSkipList();
		String last = skipList.get(skipList.size() - 1);
		int initialSize = skipList.size();
		print(skipList);

		skipList.remove(mostRightValue);
		skipList.remove(last);

		print(skipList);
		assertEquals(initialSize - 1, skipList.size());
		assertFalse(skipList.contains(last));
		}

		@Test
		void checkSortedOnLowestLayer() {
		SkipList<String> skipList = new SkipList<>();
		@DisplayName("Elements should be sorted at base level")
		void testSortedOrderOnBaseLevel() {
		String[] values = {"d", "b", "a", "c"};
		Arrays.stream(values).forEach(skipList::add);
		print(skipList);

		String[] actualOrder = IntStream.range(0, values.length).mapToObj(skipList::get).toArray(String[] ::new);

		assertArrayEquals(new String[] {"a", "b", "c", "d"}, actualOrder);
		org.junit.jupiter.api.Assertions.assertArrayEquals(new String[] {"a", "b", "c", "d"}, actualOrder);
		}

		private SkipList<String> createSkipList() {
		SkipList<String> skipList = new SkipList<>();
		String[] values = {
		"a",
		"b",
		"c",
		"d",
		"e",
		"f",
		"g",
		"h",
		"i",
		"j",
		"k",
		};
		@Test
		@DisplayName("Duplicate elements can be added and count correctly")
		void testAddDuplicates() {
		skipList.add("x");
		skipList.add("x");
		assertEquals(2, skipList.size());
		assertEquals("x", skipList.get(0));
		assertEquals("x", skipList.get(1));
		}

		@Test
		@DisplayName("Add multiple and remove all")
		void testClearViaRemovals() {
		String[] values = {"a", "b", "c"};
		Arrays.stream(values).forEach(skipList::add);
		return skipList;

		for (String v : values) {
		skipList.remove(v);
		}

		assertEquals(0, skipList.size());
		}

		/**
		* Print Skip List representation to console.
		* Optional method not involved in testing process. Used only for visualisation purposes.
		* @param skipList to print
		*/
		private void print(SkipList<?> skipList) {
		System.out.println(skipList);
		private SkipList<String> createSkipList() {
		SkipList<String> s = new SkipList<>();
		String[] values = {"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"};
		Arrays.stream(values).forEach(s::add);
		return s;
		}
		}