Enhance docs, add more tests in IntegerToEnglish (#5924)

DIRECTORY.md

@@ -64,12 +64,15 @@
             * [AffineCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AffineCipher.java)
             * [AtbashCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AtbashCipher.java)
             * [Autokey](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Autokey.java)
+            * [BaconianCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/BaconianCipher.java)
             * [Blowfish](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Blowfish.java)
             * [Caesar](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Caesar.java)
             * [ColumnarTranspositionCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ColumnarTranspositionCipher.java)
             * [DES](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/DES.java)
+            * [DiffieHellman](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/DiffieHellman.java)
             * [ECC](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ECC.java)
             * [HillCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/HillCipher.java)
+            * [MonoAlphabetic](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/MonoAlphabetic.java)
             * [PlayfairCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java)
             * [Polybius](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Polybius.java)
             * [ProductCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ProductCipher.java)
@@ -311,6 +314,8 @@
             * [ConvexHull](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/geometry/ConvexHull.java)
             * [GrahamScan](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/geometry/GrahamScan.java)
             * [Point](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/geometry/Point.java)
+          * graph
+            * [StronglyConnectedComponentOptimized](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/graph/StronglyConnectedComponentOptimized.java)
           * greedyalgorithms
             * [ActivitySelection](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/ActivitySelection.java)
             * [BinaryAddition](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/greedyalgorithms/BinaryAddition.java)
@@ -564,6 +569,7 @@
             * [UnionFind](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/UnionFind.java)
             * [UpperBound](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/searches/UpperBound.java)
           * sorts
+            * [AdaptiveMergeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/AdaptiveMergeSort.java)
             * [BeadSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/BeadSort.java)
             * [BinaryInsertionSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/BinaryInsertionSort.java)
             * [BitonicSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/BitonicSort.java)
@@ -603,6 +609,7 @@
             * [SortUtils](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/SortUtils.java)
             * [SortUtilsRandomGenerator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/SortUtilsRandomGenerator.java)
             * [SpreadSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/SpreadSort.java)
+            * [StalinSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/StalinSort.java)
             * [StoogeSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/StoogeSort.java)
             * [StrandSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/StrandSort.java)
             * [SwapSort](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/sorts/SwapSort.java)
@@ -616,6 +623,7 @@
             * [CelebrityFinder](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/CelebrityFinder.java)
             * [DecimalToAnyUsingStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DecimalToAnyUsingStack.java)
             * [DuplicateBrackets](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/DuplicateBrackets.java)
+            * [GreatestElementConstantTime](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/GreatestElementConstantTime.java)
             * [InfixToPostfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/InfixToPostfix.java)
             * [InfixToPrefix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/InfixToPrefix.java)
             * [LargestRectangle](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/LargestRectangle.java)
@@ -624,10 +632,12 @@
             * [MinStackUsingTwoStacks](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/MinStackUsingTwoStacks.java)
             * [NextGreaterElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextGreaterElement.java)
             * [NextSmallerElement](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/NextSmallerElement.java)
+            * [PalindromeWithStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PalindromeWithStack.java)
             * [PostfixEvaluator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixEvaluator.java)
             * [PostfixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PostfixToInfix.java)
             * [PrefixEvaluator](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PrefixEvaluator.java)
             * [PrefixToInfix](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/PrefixToInfix.java)
+            * [SmallestElementConstantTime](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/SmallestElementConstantTime.java)
             * [SortStack](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/SortStack.java)
             * [StackPostfixNotation](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/StackPostfixNotation.java)
             * [StackUsingTwoQueues](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/stacks/StackUsingTwoQueues.java)
@@ -726,12 +736,15 @@
             * [AffineCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AffineCipherTest.java)
             * [AtbashTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AtbashTest.java)
             * [AutokeyTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AutokeyTest.java)
+            * [BaconianCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/BaconianCipherTest.java)
             * [BlowfishTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/BlowfishTest.java)
             * [CaesarTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/CaesarTest.java)
             * [ColumnarTranspositionCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/ColumnarTranspositionCipherTest.java)
             * [DESTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/DESTest.java)
+            * [DiffieHellmanTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/DiffieHellmanTest.java)
             * [ECCTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/ECCTest.java)
             * [HillCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/HillCipherTest.java)
+            * [MonoAlphabeticTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/MonoAlphabeticTest.java)
             * [PlayfairTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java)
             * [PolybiusTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PolybiusTest.java)
             * [RailFenceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/RailFenceTest.java)
@@ -914,6 +927,8 @@
             * [BresenhamLineTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/geometry/BresenhamLineTest.java)
             * [ConvexHullTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/geometry/ConvexHullTest.java)
             * [GrahamScanTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/geometry/GrahamScanTest.java)
+          * graph
+            * [StronglyConnectedComponentOptimizedTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/graph/StronglyConnectedComponentOptimizedTest.java)
           * greedyalgorithms
             * [ActivitySelectionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/ActivitySelectionTest.java)
             * [BinaryAdditionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/greedyalgorithms/BinaryAdditionTest.java)
@@ -1133,6 +1148,7 @@
             * [UnionFindTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/UnionFindTest.java)
             * [UpperBoundTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/searches/UpperBoundTest.java)
           * sorts
+            * [AdaptiveMergeSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/AdaptiveMergeSortTest.java)
             * [BeadSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/BeadSortTest.java)
             * [BinaryInsertionSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/BinaryInsertionSortTest.java)
             * [BitonicSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/BitonicSortTest.java)
@@ -1171,6 +1187,7 @@
             * [SortUtilsRandomGeneratorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/SortUtilsRandomGeneratorTest.java)
             * [SortUtilsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/SortUtilsTest.java)
             * [SpreadSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/SpreadSortTest.java)
+            * [StalinSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/StalinSortTest.java)
             * [StoogeSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/StoogeSortTest.java)
             * [StrandSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/StrandSortTest.java)
             * [SwapSortTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/sorts/SwapSortTest.java)
@@ -1184,6 +1201,7 @@
             * [CelebrityFinderTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/CelebrityFinderTest.java)
             * [DecimalToAnyUsingStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/DecimalToAnyUsingStackTest.java)
             * [DuplicateBracketsTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/DuplicateBracketsTest.java)
+            * [GreatestElementConstantTimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/GreatestElementConstantTimeTest.java)
             * [InfixToPostfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/InfixToPostfixTest.java)
             * [InfixToPrefixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/InfixToPrefixTest.java)
             * [LargestRectangleTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/LargestRectangleTest.java)
@@ -1191,10 +1209,12 @@
             * [MinStackUsingTwoStacksTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/MinStackUsingTwoStacksTest.java)
             * [NextGreaterElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/NextGreaterElementTest.java)
             * [NextSmallerElementTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/NextSmallerElementTest.java)
+            * [PalindromeWithStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PalindromeWithStackTest.java)
             * [PostfixEvaluatorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PostfixEvaluatorTest.java)
             * [PostfixToInfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PostfixToInfixTest.java)
             * [PrefixEvaluatorTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PrefixEvaluatorTest.java)
             * [PrefixToInfixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/PrefixToInfixTest.java)
+            * [SmallestElementConstantTimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/SmallestElementConstantTimeTest.java)
             * [SortStackTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/SortStackTest.java)
             * [StackPostfixNotationTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/StackPostfixNotationTest.java)
             * [StackUsingTwoQueuesTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/stacks/StackUsingTwoQueuesTest.java)

src/main/java/com/thealgorithms/conversions/IntegerToEnglish.java

@@ -2,7 +2,28 @@ package com.thealgorithms.conversions;
 
 import java.util.Map;
 
+/**
+ * A utility class to convert integers to their English word representation.
+ *
+ * <p>The class supports conversion of numbers from 0 to 2,147,483,647
+ * (the maximum value of a 32-bit signed integer). It divides the number
+ * into groups of three digits (thousands, millions, billions, etc.) and
+ * translates each group into words.</p>
+ *
+ * <h2>Example Usage</h2>
+ * <pre>
+ *   IntegerToEnglish.integerToEnglishWords(12345);
+ *   // Output: "Twelve Thousand Three Hundred Forty Five"
+ * </pre>
+ *
+ * <p>This class uses two maps:</p>
+ * <ul>
+ *   <li>BASE_NUMBERS_MAP: Holds English words for numbers 0-20, multiples of 10 up to 90, and 100.</li>
+ *   <li>THOUSAND_POWER_MAP: Maps powers of 1000 (e.g., Thousand, Million, Billion).</li>
+ * </ul>
+ */
 public final class IntegerToEnglish {
+
     private static final Map<Integer, String> BASE_NUMBERS_MAP = Map.ofEntries(Map.entry(0, ""), Map.entry(1, "One"), Map.entry(2, "Two"), Map.entry(3, "Three"), Map.entry(4, "Four"), Map.entry(5, "Five"), Map.entry(6, "Six"), Map.entry(7, "Seven"), Map.entry(8, "Eight"), Map.entry(9, "Nine"),
         Map.entry(10, "Ten"), Map.entry(11, "Eleven"), Map.entry(12, "Twelve"), Map.entry(13, "Thirteen"), Map.entry(14, "Fourteen"), Map.entry(15, "Fifteen"), Map.entry(16, "Sixteen"), Map.entry(17, "Seventeen"), Map.entry(18, "Eighteen"), Map.entry(19, "Nineteen"), Map.entry(20, "Twenty"),
         Map.entry(30, "Thirty"), Map.entry(40, "Forty"), Map.entry(50, "Fifty"), Map.entry(60, "Sixty"), Map.entry(70, "Seventy"), Map.entry(80, "Eighty"), Map.entry(90, "Ninety"), Map.entry(100, "Hundred"));
@@ -13,35 +34,46 @@ public final class IntegerToEnglish {
     }
 
     /**
-        converts numbers < 1000 to english words
+     * Converts numbers less than 1000 into English words.
+     *
+     * @param number the integer value (0-999) to convert
+     * @return the English word representation of the input number
      */
     private static String convertToWords(int number) {
         int remainder = number % 100;
-
+        StringBuilder result = new StringBuilder();
-        String result;
 
         if (remainder <= 20) {
-            result = BASE_NUMBERS_MAP.get(remainder);
+            result.append(BASE_NUMBERS_MAP.get(remainder));
         } else if (BASE_NUMBERS_MAP.containsKey(remainder)) {
-            result = BASE_NUMBERS_MAP.get(remainder);
+            result.append(BASE_NUMBERS_MAP.get(remainder));
         } else {
             int tensDigit = remainder / 10;
             int onesDigit = remainder % 10;
-
+            String tens = BASE_NUMBERS_MAP.getOrDefault(tensDigit * 10, "");
-            result = String.format("%s %s", BASE_NUMBERS_MAP.get(tensDigit * 10), BASE_NUMBERS_MAP.get(onesDigit));
+            String ones = BASE_NUMBERS_MAP.getOrDefault(onesDigit, "");
+            result.append(tens);
+            if (ones != null && !ones.isEmpty()) {
+                result.append(" ").append(ones);
+            }
         }
 
         int hundredsDigit = number / 100;
-
         if (hundredsDigit > 0) {
-            result = String.format("%s %s%s", BASE_NUMBERS_MAP.get(hundredsDigit), BASE_NUMBERS_MAP.get(100), result.isEmpty() ? "" : " " + result);
+            if (result.length() > 0) {
+                result.insert(0, " ");
+            }
+            result.insert(0, String.format("%s Hundred", BASE_NUMBERS_MAP.get(hundredsDigit)));
         }
 
-        return result;
+        return result.toString().trim();
     }
 
     /**
-      Only convert groups of three digit if they are non-zero
+     * Converts a non-negative integer to its English word representation.
+     *
+     * @param number the integer to convert (0-2,147,483,647)
+     * @return the English word representation of the input number
      */
     public static String integerToEnglishWords(int number) {
         if (number == 0) {
@@ -49,7 +81,6 @@ public final class IntegerToEnglish {
         }
 
         StringBuilder result = new StringBuilder();
-
         int index = 0;
 
         while (number > 0) {
@@ -58,23 +89,20 @@ public final class IntegerToEnglish {
 
             if (remainder > 0) {
                 String subResult = convertToWords(remainder);
-
                 if (!subResult.isEmpty()) {
-                    if (!result.isEmpty()) {
-                        result.insert(0, subResult + " " + THOUSAND_POWER_MAP.get(index) + " ");
-                    } else {
                     if (index > 0) {
-                            result = new StringBuilder(subResult + " " + THOUSAND_POWER_MAP.get(index));
+                        subResult += " " + THOUSAND_POWER_MAP.get(index);
-                        } else {
-                            result = new StringBuilder(subResult);
                     }
+                    if (result.length() > 0) {
+                        result.insert(0, " ");
                     }
+                    result.insert(0, subResult);
                 }
             }
 
             index++;
         }
 
-        return result.toString();
+        return result.toString().trim();
     }
 }

src/test/java/com/thealgorithms/conversions/IntegerToEnglishTest.java

@@ -11,5 +11,36 @@ public class IntegerToEnglishTest {
         assertEquals("Two Billion One Hundred Forty Seven Million Four Hundred Eighty Three Thousand Six Hundred Forty Seven", IntegerToEnglish.integerToEnglishWords(2147483647));
         assertEquals("One Million Two Hundred Thirty Four Thousand Five Hundred Sixty Seven", IntegerToEnglish.integerToEnglishWords(1234567));
         assertEquals("Twelve Thousand Three Hundred Forty Five", IntegerToEnglish.integerToEnglishWords(12345));
+        assertEquals("One Hundred", IntegerToEnglish.integerToEnglishWords(100));
+        assertEquals("Zero", IntegerToEnglish.integerToEnglishWords(0));
+    }
+
+    @Test
+    public void testSmallNumbers() {
+        assertEquals("Ten", IntegerToEnglish.integerToEnglishWords(10));
+        assertEquals("Nineteen", IntegerToEnglish.integerToEnglishWords(19));
+        assertEquals("Twenty One", IntegerToEnglish.integerToEnglishWords(21));
+        assertEquals("Ninety Nine", IntegerToEnglish.integerToEnglishWords(99));
+    }
+
+    @Test
+    public void testHundreds() {
+        assertEquals("One Hundred One", IntegerToEnglish.integerToEnglishWords(101));
+        assertEquals("Five Hundred Fifty", IntegerToEnglish.integerToEnglishWords(550));
+        assertEquals("Nine Hundred Ninety Nine", IntegerToEnglish.integerToEnglishWords(999));
+    }
+
+    @Test
+    public void testThousands() {
+        assertEquals("One Thousand", IntegerToEnglish.integerToEnglishWords(1000));
+        assertEquals("Ten Thousand One", IntegerToEnglish.integerToEnglishWords(10001));
+        assertEquals("Seventy Six Thousand Five Hundred Forty Three", IntegerToEnglish.integerToEnglishWords(76543));
+    }
+
+    @Test
+    public void testEdgeCases() {
+        assertEquals("One Million", IntegerToEnglish.integerToEnglishWords(1_000_000));
+        assertEquals("One Billion", IntegerToEnglish.integerToEnglishWords(1_000_000_000));
+        assertEquals("Two Thousand", IntegerToEnglish.integerToEnglishWords(2000));
     }
 }