resolving (BAEL-5148) Get String Character by Index in Java (eugenp#1…

…1340)

* resolving (BAEL-5148) Get String Character by Index in Java

* changing method name from *_thenCorrect() to *_thenSuccess()

* reverted README changes according to the editor suggestion

* extra snippet removed inorder to comply with the article edits

core-java-modules/core-java-string-apis/src/test/java/com/baeldung/stringapi/StringCharAtUnitTest.java

@@ -0,0 +1,29 @@
+package com.baeldung.stringapi;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+public class StringCharAtUnitTest {
+    @Test
+    public void whenCallCharAt_thenSuccess() {
+        String sample = "abcdefg";
+        assertEquals('d', sample.charAt(3));
+    }
+
+    @Test()
+    public void whenCharAtNonExist_thenIndexOutOfBoundsExceptionThrown() {
+        String sample = "abcdefg";
+        assertThrows(IndexOutOfBoundsException.class, () -> sample.charAt(-1));
+        assertThrows(IndexOutOfBoundsException.class, () -> sample.charAt(sample.length()));
+    }
+
+    @Test
+    public void whenCallCharAt_thenReturnString() {
+        String sample = "abcdefg";
+        assertEquals("a", Character.toString(sample.charAt(0)));
+        assertEquals("a", String.valueOf(sample.charAt(0)));
+    }
+
+}