This commit is related to BAEL-7342 (#15460)

This commit aims to add a test class "CheckIfStringBuilderContainsCharUnitTest" that suggests several ways to check if a StringBuilder has a char or not.

core-java-modules/core-java-string-operations-7/src/test/java/com/baeldung/stringbuilderhaschar/CheckIfStringBuilderContainsCharUnitTest.java

@@ -0,0 +1,44 @@
+package com.baeldung.stringbuilderhaschar;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+public class CheckIfStringBuilderContainsCharUnitTest {
+
+    StringBuilder stringBuilder = new StringBuilder("Welcome to Baeldung Java Tutorial!");
+    char targetChar = 'o';
+
+    @Test
+    public void givenStringBuilder_whenUsingIndexOfMethod_thenCheckIfSCharExists() {
+        int index = stringBuilder.indexOf(String.valueOf(targetChar));
+        assertTrue(index != -1);
+    }
+
+    @Test
+    public void givenStringBuilder_whenUsingContainsMethod_thenCheckIfSCharExists() {
+        boolean containsChar = stringBuilder.toString().contains(String.valueOf(targetChar));
+        assertTrue(containsChar);
+    }
+
+    @Test
+    public void givenStringBuilder_whenUsingJavaStream_thenCheckIfSCharExists() {
+        boolean charFound = stringBuilder.chars().anyMatch(c -> c == targetChar);
+
+        assertTrue(charFound);
+    }
+
+    @Test
+    public void givenStringBuilder_whenUsingIterations_thenCheckIfSCharExists() {
+        boolean charFound = false;
+
+        for (int i = 0; i < stringBuilder.length(); i++) {
+            if (stringBuilder.charAt(i) == targetChar) {
+                charFound = true;
+                break;
+            }
+        }
+
+        assertTrue(charFound);
+    }
+}