test: add comprehensive MyHashMap tests

second-part/hw-01/src/app/src/test/java/org/example/MyHashMapTest.java

@@ -118,4 +118,202 @@ class MyHashMapTest {
     assertEquals(100, map.remove(null));
     assertNull(map.get(null));
   }
+
+  @Test
+  void shouldHandleNullValue() {
+    MyHashMap<String, Integer> map = new MyHashMap<>(4);
+
+    assertNull(map.put("A", null));
+    assertNull(map.get("A"));
+
+    assertNull(map.put("A", 10));
+    assertEquals(10, map.get("A"));
+  }
+
+  @Test
+  void shouldUpdateNullValue() {
+    MyHashMap<String, Integer> map = new MyHashMap<>(4);
+
+    map.put("A", 10);
+
+    assertEquals(10, map.put("A", null));
+    assertNull(map.get("A"));
+  }
+
+  @Test
+  void shouldRemoveMiddleElementFromCollisionChain() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(4);
+
+    map.put(1, "A");
+    map.put(5, "B");
+    map.put(9, "C");
+
+    assertEquals("B", map.remove(5));
+
+    assertEquals("A", map.get(1));
+    assertNull(map.get(5));
+    assertEquals("C", map.get(9));
+  }
+
+  @Test
+  void shouldRemoveLastElementFromCollisionChain() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(4);
+
+    map.put(1, "A");
+    map.put(5, "B");
+    map.put(9, "C");
+
+    assertEquals("C", map.remove(9));
+
+    assertEquals("A", map.get(1));
+    assertEquals("B", map.get(5));
+    assertNull(map.get(9));
+  }
+
+  @Test
+  void shouldReinsertRemovedKey() {
+    MyHashMap<String, Integer> map = new MyHashMap<>(4);
+
+    map.put("A", 10);
+    assertEquals(10, map.remove("A"));
+
+    assertNull(map.get("A"));
+    assertNull(map.put("A", 20));
+    assertEquals(20, map.get("A"));
+  }
+
+  @Test
+  void shouldKeepCollidingEntriesAfterRemovingFirst() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(4);
+
+    map.put(1, "A");
+    map.put(5, "B");
+    map.put(9, "C");
+
+    map.remove(1);
+
+    assertEquals("B", map.get(5));
+    assertEquals("C", map.get(9));
+  }
+
+  @Test
+  void shouldKeepCollidingEntriesAfterRemovingMiddle() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(4);
+
+    map.put(1, "A");
+    map.put(5, "B");
+    map.put(9, "C");
+    map.put(13, "D");
+
+    map.remove(5);
+
+    assertEquals("A", map.get(1));
+    assertEquals("C", map.get(9));
+    assertEquals("D", map.get(13));
+  }
+
+  @Test
+  void shouldHandleManyCollisions() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(2);
+
+    map.put(1, "A");
+    map.put(3, "B");
+    map.put(5, "C");
+    map.put(7, "D");
+    map.put(9, "E");
+
+    assertEquals("A", map.get(1));
+    assertEquals("B", map.get(3));
+    assertEquals("C", map.get(5));
+    assertEquals("D", map.get(7));
+    assertEquals("E", map.get(9));
+  }
+
+  @Test
+  void shouldResizeAndKeepCollisions() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(2);
+
+    map.put(1, "A");
+    map.put(3, "B");
+    map.put(5, "C");
+    map.put(7, "D");
+    map.put(9, "E");
+    map.put(11, "F");
+
+    assertEquals("A", map.get(1));
+    assertEquals("B", map.get(3));
+    assertEquals("C", map.get(5));
+    assertEquals("D", map.get(7));
+    assertEquals("E", map.get(9));
+    assertEquals("F", map.get(11));
+  }
+
+  @Test
+  void shouldUpdateCollidingKey() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(4);
+
+    map.put(1, "A");
+    map.put(5, "B");
+    map.put(9, "C");
+
+    assertEquals("B", map.put(5, "NEW"));
+
+    assertEquals("A", map.get(1));
+    assertEquals("NEW", map.get(5));
+    assertEquals("C", map.get(9));
+  }
+
+  @Test
+  void shouldHandleEqualButDifferentStringInstances() {
+    MyHashMap<String, Integer> map = new MyHashMap<>(4);
+
+    map.put(new String("A"), 10);
+
+    assertEquals(10, map.get(new String("A")));
+    assertEquals(10, map.remove(new String("A")));
+  }
+
+  @Test
+  void shouldNotAffectOtherKeysWhenUpdating() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(4);
+
+    map.put(1, "A");
+    map.put(2, "B");
+    map.put(3, "C");
+
+    map.put(2, "UPDATED");
+
+    assertEquals("A", map.get(1));
+    assertEquals("UPDATED", map.get(2));
+    assertEquals("C", map.get(3));
+  }
+
+  @Test
+  void shouldNotFindKeyAfterRemoveAndResize() {
+    MyHashMap<Integer, String> map = new MyHashMap<>(2);
+
+    map.put(1, "A");
+    map.put(2, "B");
+    map.put(3, "C");
+    map.put(4, "D");
+
+    map.remove(2);
+
+    assertNull(map.get(2));
+    assertEquals("A", map.get(1));
+    assertEquals("C", map.get(3));
+    assertEquals("D", map.get(4));
+  }
+
+  @Test
+  void shouldHandleRepeatedPutAndRemove() {
+    MyHashMap<String, Integer> map = new MyHashMap<>(4);
+
+    for (int i = 0; i < 100; i++) {
+      assertNull(map.put("A", i));
+      assertEquals(i, map.get("A"));
+      assertEquals(i, map.remove("A"));
+      assertNull(map.get("A"));
+    }
+  }
 }