diff --git a/src/main/java/com/thealgorithms/maths/NumberOfDigits.java b/src/main/java/com/thealgorithms/maths/NumberOfDigits.java
index 665d8ef5a98c..fc538196c7da 100644
--- a/src/main/java/com/thealgorithms/maths/NumberOfDigits.java
+++ b/src/main/java/com/thealgorithms/maths/NumberOfDigits.java
@@ -3,35 +3,16 @@
 /**
  * Find the number of digits in a number.
  */
-public class NumberOfDigits {
-
-    public static void main(String[] args) {
-        int[] numbers = {
-            0,
-            12,
-            123,
-            1234,
-            -12345,
-            123456,
-            1234567,
-            12345678,
-            123456789,
-        };
-        for (int i = 0; i < numbers.length; ++i) {
-            assert numberOfDigits(numbers[i]) == i + 1;
-            assert numberOfDigitsFast(numbers[i]) == i + 1;
-            assert numberOfDigitsFaster(numbers[i]) == i + 1;
-            assert numberOfDigitsRecursion(numbers[i]) == i + 1;
-        }
+public final class NumberOfDigits {
+    private NumberOfDigits() {
     }
-
     /**
      * Find the number of digits in a number.
      *
      * @param number number to find
      * @return number of digits of given number
      */
-    private static int numberOfDigits(int number) {
+    public static int numberOfDigits(int number) {
         int digits = 0;
         do {
             digits++;
@@ -46,7 +27,7 @@ private static int numberOfDigits(int number) {
      * @param number number to find
      * @return number of digits of given number
      */
-    private static int numberOfDigitsFast(int number) {
+    public static int numberOfDigitsFast(int number) {
         return number == 0 ? 1 : (int) Math.floor(Math.log10(Math.abs(number)) + 1);
     }
 
@@ -56,7 +37,7 @@ private static int numberOfDigitsFast(int number) {
      * @param number number to find
      * @return number of digits of given number
      */
-    private static int numberOfDigitsFaster(int number) {
+    public static int numberOfDigitsFaster(int number) {
         return number < 0 ? (-number + "").length() : (number + "").length();
     }
 
@@ -66,7 +47,7 @@ private static int numberOfDigitsFaster(int number) {
      * @param number number to find
      * @return number of digits of given number
      */
-    private static int numberOfDigitsRecursion(int number) {
+    public static int numberOfDigitsRecursion(int number) {
         return number / 10 == 0 ? 1 : 1 + numberOfDigitsRecursion(number / 10);
     }
 }
diff --git a/src/test/java/com/thealgorithms/maths/NumberOfDigitsTest.java b/src/test/java/com/thealgorithms/maths/NumberOfDigitsTest.java
new file mode 100644
index 000000000000..2e807db12fb9
--- /dev/null
+++ b/src/test/java/com/thealgorithms/maths/NumberOfDigitsTest.java
@@ -0,0 +1,40 @@
+package com.thealgorithms.maths;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import java.util.function.IntFunction;
+import java.util.stream.Stream;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class NumberOfDigitsTest {
+
+    @ParameterizedTest
+    @MethodSource("testCases")
+    void testNumberOfDigits(final int expected, final int number, final IntFunction<Integer> methodUnderTest) {
+        assertEquals(expected, methodUnderTest.apply(number));
+        assertEquals(expected, methodUnderTest.apply(-number));
+    }
+
+    private static Stream<Arguments> testCases() {
+        final Integer[][] inputs = new Integer[][] {
+            {3, 100},
+            {1, 0},
+            {2, 12},
+            {3, 123},
+            {4, 1234},
+            {5, 12345},
+            {6, 123456},
+            {7, 1234567},
+            {8, 12345678},
+            {9, 123456789},
+            {9, 987654321},
+        };
+
+        final IntFunction<Integer>[] methods = new IntFunction[] {NumberOfDigits::numberOfDigits, NumberOfDigits::numberOfDigitsFast, NumberOfDigits::numberOfDigitsFaster, NumberOfDigits::numberOfDigitsRecursion};
+
+        return Stream.of(inputs).flatMap(input -> Stream.of(methods).map(method -> Arguments.of(input[0], input[1], method)));
+    }
+}