Cover BSTRecursive with tests (#4180)

src/test/java/com/thealgorithms/datastructures/trees/BSTRecursiveTest.java

@@ -0,0 +1,61 @@
+package com.thealgorithms.datastructures.trees;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+/**
+ * @author Albina Gimaletdinova on 06/05/2023
+ */
+public class BSTRecursiveTest {
+    @Test
+    public void testBSTIsCorrectlyConstructedFromOneNode() {
+        BSTRecursive tree = new BSTRecursive();
+        tree.add(6);
+
+        Assertions.assertTrue(CheckBinaryTreeIsValidBST.isBST(tree.getRoot()));
+    }
+
+    @Test
+    public void testBSTIsCorrectlyCleanedAndEmpty() {
+        BSTRecursive tree = new BSTRecursive();
+
+        tree.add(6);
+        tree.remove(6);
+
+        tree.add(12);
+        tree.add(1);
+        tree.add(2);
+
+        tree.remove(1);
+        tree.remove(2);
+        tree.remove(12);
+
+        Assertions.assertNull(tree.getRoot());
+    }
+
+    @Test
+    public void testBSTIsCorrectlyCleanedAndNonEmpty() {
+        BSTRecursive tree = new BSTRecursive();
+
+        tree.add(6);
+        tree.remove(6);
+
+        tree.add(12);
+        tree.add(1);
+        tree.add(2);
+
+        Assertions.assertTrue(CheckBinaryTreeIsValidBST.isBST(tree.getRoot()));
+    }
+
+    @Test
+    public void testBSTIsCorrectlyConstructedFromMultipleNodes() {
+        BSTRecursive tree = new BSTRecursive();
+        tree.add(7);
+        tree.add(1);
+        tree.add(5);
+        tree.add(100);
+        tree.add(50);
+
+        Assertions.assertTrue(CheckBinaryTreeIsValidBST.isBST(tree.getRoot()));
+    }
+}