diff --git a/src/main/java/StringManipulation.java b/src/main/java/StringManipulation.java
index 4deb6f1..53f45de 100644
--- a/src/main/java/StringManipulation.java
+++ b/src/main/java/StringManipulation.java
@@ -1,33 +1,124 @@
+//Alvin Bautista
+//CS 410 - JUNIT Assignment
+//06112023
+
 public class StringManipulation implements StringManipulationInterface {
 
+    private String string; //stores the string to manipulate
+
     @Override
     public String getString() {
-        return null;
+        return this.string; //return the string stored in this object
     }
 
     @Override
     public void setString(String string) {
+        this.string = string; //set the string stored in this object
     }
 
     @Override
     public int count() {
-        return 0;
+        //check if the string is null or empty
+        if (this.string == null || this.string.trim().isEmpty()) {
+            return 0;
+        }
+        //split the string into words and return the number of words
+        return this.string.trim().split("\\s+").length;
     }
 
     @Override
     public String removeNthCharacter(int n, boolean maintainSpacing) {
-        return null;
+        //validate n
+        if (n <= 0) {
+            throw new IllegalArgumentException("n should be greater than 0");
+        }
+
+        //special case when n is 1
+        if (n == 1) {
+            return this.string; //return original string
+        }
+
+        //validate the string
+        if (this.string == null) {
+            throw new IndexOutOfBoundsException("String is null");
+        }
+
+        //validate that n is not greater than string length
+        if (n > this.string.length()) {
+            throw new IndexOutOfBoundsException("n is greater than the string length");
+        }
+
+        //initialize a StringBuilder to build the result
+        StringBuilder result = new StringBuilder();
+
+        //loop through characters of the string
+        for (int i = 1; i <= this.string.length(); i++) {
+            //append character to result if its position is not a multiple of n
+            if (i % n != 0) {
+                result.append(this.string.charAt(i - 1));
+            } else {
+                //append space to result if maintainSpacing is true and position is multiple of n
+                if (maintainSpacing) {
+                    result.append(' ');
+                }
+            }
+        }
+
+        //return the resulting string
+        return result.toString();
     }
 
     @Override
     public String[] getSubStrings(int startWord, int endWord) {
-        return null;
+        //validate startWord and endWord
+        if (startWord <= 0 || endWord <= 0 || startWord > endWord) {
+            throw new IllegalArgumentException("Invalid startWord or endWord");
+        }
+
+        //validate the string
+        if (this.string == null) {
+            throw new IndexOutOfBoundsException("String is null");
+        }
+
+        //split string into words
+        String[] words = this.string.split("\\s+");
+
+        //check if there are enough words to get the substring
+        if (endWord > words.length) {
+            throw new IndexOutOfBoundsException("String has fewer than endWord words");
+        }
+
+        //create array to store the substrings
+        String[] subStrings = new String[endWord - startWord + 1];
+
+        //copy the substrings into the array
+        System.arraycopy(words, startWord - 1, subStrings, 0, subStrings.length);
+
+        //return the substrings array
+        return subStrings;
     }
 
     @Override
     public String restoreString(int[] indices) {
-        return null;
-    }
+        //validate the indices and the string
+        if (indices == null || this.string == null || indices.length != this.string.length() || indices.length == 0) {
+            throw new IllegalArgumentException("String and indices should have the same non-zero length");
+        }
 
+        //create an array to store characters in the restored order
+        char[] restored = new char[this.string.length()];
 
+        //loop through the indices
+        for (int i = 0; i < indices.length; i++) {
+            //validate each index
+            if (indices[i] < 0 || indices[i] >= this.string.length()) {
+                throw new IndexOutOfBoundsException("Index out of bounds");
+            }
+            //place each character at the correct position according to the indices array
+            restored[indices[i]] = this.string.charAt(i);
+        }
+
+        //return the restored string
+        return new String(restored);
+    }
 }
diff --git a/src/test/java/StringManipulationTest.java b/src/test/java/StringManipulationTest.java
index 6692c2c..7c261da 100644
--- a/src/test/java/StringManipulationTest.java
+++ b/src/test/java/StringManipulationTest.java
@@ -1,149 +1,200 @@
+//Alvin Bautista
+//CS 410 - JUNIT Assignment
+//06112023
+
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
-
 import static org.junit.jupiter.api.Assertions.*;
 
 public class StringManipulationTest {
 
-    private StringManipulationInterface manipulatedstring;
+    private StringManipulationInterface manipulatedString; //object to be tested
 
     @BeforeEach
     public void setUp() {
-        manipulatedstring = new StringManipulation();
+        manipulatedString = new StringManipulation(); //initialize object before each test
     }
 
     @AfterEach
     public void tearDown() {
-        manipulatedstring = null;
+        manipulatedString = null; //cleanup after each test
     }
 
     @Test
     public void testCount1() {
-        manipulatedstring.setString("This is my string");
-        int length = manipulatedstring.count();
-        assertEquals(4, length);
+        manipulatedString.setString("This is my string"); //setting string
+        int length = manipulatedString.count(); //count words
+        assertEquals(4, length); //assert expected value
     }
 
     @Test
     public void testCount2() {
-        fail("Not yet implemented");
+        manipulatedString.setString("One more test case"); //setting string
+        assertEquals(4, manipulatedString.count()); //directly asserting expected value
     }
 
     @Test
     public void testCount3() {
-        fail("Not yet implemented");
+        manipulatedString.setString(""); //setting empty string
+        assertEquals(0, manipulatedString.count()); //asserting count is 0
     }
 
     @Test
     public void testCount4() {
-        fail("Not yet implemented");
+        manipulatedString.setString("Single"); //setting single word
+        assertEquals(1, manipulatedString.count()); //asserting count is 1
     }
 
     @Test
     public void testRemoveNthCharacter1() {
-        manipulatedstring.setString("I'd b3tt3r put s0me d161ts in this 5tr1n6, right?");
-        assertEquals("I' bttr uts0e 16tsinths trn6 rgh?", manipulatedstring.removeNthCharacter(3, false));
+        manipulatedString.setString("I'd b3tt3r put s0me d161ts in this 5tr1n6, right?"); //setting string
+        assertEquals("I' bttr uts0e 16tsinths trn6 rgh?", manipulatedString.removeNthCharacter(3, false)); //asserting removal of characters
     }
 
     @Test
     public void testRemoveNthCharacter2() {
-        manipulatedstring.setString("I'd b3tt3r put s0me d161ts in this 5tr1n6, right?");
-        assertEquals("I'  b tt r  ut s0 e  16 ts in th s  tr n6  r gh ?", manipulatedstring.removeNthCharacter(3, true));
+        manipulatedString.setString("I'd b3tt3r put s0me d161ts in this 5tr1n6, right?"); //setting string
+        assertEquals("I'  b tt r  ut s0 e  16 ts in th s  tr n6  r gh ?", manipulatedString.removeNthCharacter(3, true)); //asserting removal with spaces
     }
 
     @Test
     public void testRemoveNthCharacter3() {
-        fail("Not yet implemented");
+        manipulatedString.setString("Example text for test case."); //setting string
+        assertEquals("Eapetx o etcs.", manipulatedString.removeNthCharacter(2, false)); //asserting removal of characters
     }
 
     @Test
     public void testRemoveNthCharacter4() {
-        fail("Not yet implemented");
+        manipulatedString.setString("Example text for test case."); //setting string
+        assertEquals("Example text for test case.", manipulatedString.removeNthCharacter(1, false)); //asserting no change for n=1
     }
 
     @Test
     public void testRemoveNthCharacter5() {
-        fail("Not yet implemented");
+        manipulatedString.setString("Small"); //setting string
+        assertEquals("Sal", manipulatedString.removeNthCharacter(2, false)); //asserting removal of characters
     }
 
     @Test
     public void testRemoveNthCharacter6() {
-        fail("Not yet implemented");
+        manipulatedString.setString("Small"); //setting string
+        assertEquals("S a l", manipulatedString.removeNthCharacter(2, true)); //asserting removal with spaces
     }
 
     @Test
     public void testRemoveNthCharacter7() {
-        fail("Not yet implemented");
+        assertThrows(IndexOutOfBoundsException.class, () -> manipulatedString.removeNthCharacter(20, true)); //asserting exception for out of bounds
     }
 
     @Test
-    public void testGeSubStrings1() {
-        manipulatedstring.setString("This is my string");
-        String [] sStings = manipulatedstring.getSubStrings(3, 4);
+    public void testGetSubStrings1() {
+        manipulatedString.setString("This is my string"); //setting string
+        String [] sStings = manipulatedString.getSubStrings(3, 4); //get substring array
 
-        assertEquals(sStings[0], "my");
+        assertEquals(sStings[0], "my"); //asserting elements
         assertEquals(sStings[1], "string");
     }
 
     @Test
-    public void testGeSubStrings2() {
-        fail("Not yet implemented");
+    public void testGetSubStrings2() {
+        manipulatedString.setString("A B C D E"); //setting string
+        String[] subStrings = manipulatedString.getSubStrings(2, 4); //get substring array
+        assertEquals("B", subStrings[0]); //asserting elements
+        assertEquals("C", subStrings[1]);
+        assertEquals("D", subStrings[2]);
     }
+
     @Test
-    public void testGeSubStrings3() {
-        fail("Not yet implemented");
+    public void testGetSubStrings3() {
+        manipulatedString.setString("One Two"); //setting string
+        String[] subStrings = manipulatedString.getSubStrings(1, 2); //get substring array
+        assertEquals("One", subStrings[0]); //asserting elements
+        assertEquals("Two", subStrings[1]);
     }
+
     @Test
-    public void testGeSubStrings4() {
-        fail("Not yet implemented");
+    public void testGetSubStrings4() {
+        assertThrows(IllegalArgumentException.class, () -> manipulatedString.getSubStrings(3, 2)); //asserting exception for invalid arguments
     }
+
     @Test
-    public void testGeSubStrings5() {
-        fail("Not yet implemented");
+    public void testGetSubStrings5() {
+        manipulatedString.setString("Short"); //setting string
+        assertThrows(IndexOutOfBoundsException.class, () -> manipulatedString.getSubStrings(1, 2)); //asserting exception for out of bounds
     }
+
     @Test
-    public void testGeSubStrings6() {
-        fail("Not yet implemented");
+    public void testGetSubStrings6() {
+        manipulatedString.setString("Just One"); //setting string
+        String[] subStrings = manipulatedString.getSubStrings(1, 1); //get substring array
+        assertEquals("Just", subStrings[0]); //asserting element
     }
 
     @Test
-    public void testRestoreString1()
-    {
-        manipulatedstring.setString("art");
-        int [] array;
-        array=new int[]{1,0,2};
-        String restoreString = manipulatedstring.restoreString(array);
-        assertEquals(restoreString, "rat");
+    public void testRestoreString1() {
+        manipulatedString.setString("art"); //setting string
+        int[] array = {1, 0, 2}; //indices array
+        String restoreString = manipulatedString.restoreString(array); //restoring string
+        assertEquals(restoreString, "rat"); //asserting restored string
     }
 
     @Test
-    public void testRestoreString2()
-    {
-        fail("Not yet implemented");
-
+    public void testRestoreString2() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            manipulatedString.setString("invalid"); //setting string
+            int[] array = {1, 0}; //invalid indices array
+            manipulatedString.restoreString(array); //should throw exception
+        });
     }
 
     @Test
-    public void testRestoreString3()
-    {
-        fail("Not yet implemented");
-
+    public void testRestoreString3() {
+        assertThrows(IllegalArgumentException.class, () -> {
+            manipulatedString.setString("outofbounds"); //setting string
+            int[] array = {1, 0, 20}; //out of bounds indices array
+            manipulatedString.restoreString(array); //should throw exception
+        });
     }
 
     @Test
-    public void testRestoreString4()
-    {
-        fail("Not yet implemented");
-
+    public void testRestoreString4() {
+        // Test case to verify the restoreString() method when the input string is "team"
+        manipulatedString.setString("team");
+        // and the indices array is {-1, 0, 1, 2}.
+        int[] array = new int[]{-1, 0, 1, 2};
+        // It should throw an IndexOutOfBoundsException.
+        assertThrows(IndexOutOfBoundsException.class, ()->{manipulatedString.restoreString(array);});
     }
 
     @Test
-    public void testRestoreString5()
-    {
-        fail("Not yet implemented");
+    public void testRestoreString5(){
+        // Test case to verify the restoreString() method when the input string is "group"
+        manipulatedString.setString("group");
+        // and the indices array is {5, 0, 1, 2, 3}.
+        int[] array = new int[]{5, 0, 1, 2, 3};
+        // It should throw an IndexOutOfBoundsException.
+        assertThrows(IndexOutOfBoundsException.class, ()->{manipulatedString.restoreString(array);});
+    }
 
+    @Test
+    public void testRestoreString6() {
+        // Test case to verify the restoreString() method when the input string is null
+        manipulatedString.setString(null);
+        // and the indices array is {2, 3, 5, 4, 1, 0}.
+        int[] array = new int[]{2, 3, 5, 4, 1, 0};
+        // It should throw an IllegalArgumentException.
+        assertThrows(IllegalArgumentException.class, ()->{manipulatedString.restoreString(array);});
     }
 
-}
+    @Test
+    public void testRestoreString7() {
+        // Test case to verify the restoreString() method when the input string is "MASTER IS"
+        manipulatedString.setString("MASTER IS");
+        // and the indices array is {5, 4, 0, 1, 2, 3, 6, 7, 8}.
+        int[] array = new int[]{5, 4, 0, 1, 2, 3, 6, 7, 8};
+        // It should return the expected output "STERAM IS".
+        assertEquals("STERAM IS", manipulatedString.restoreString(array));
+    }
+}
\ No newline at end of file