test: CountCharTest (#5423)

test: CountCharTest

Co-authored-by: alxkm <alx@alx.com>

src/main/java/com/thealgorithms/others/CountChar.java

@@ -5,13 +5,16 @@ public final class CountChar {
     }
 
     /**
-     * Count non space character in string
+     * Counts the number of non-whitespace characters in the given string.
      *
-     * @param str String to count the characters
-     * @return number of character in the specified string
+     * @param str the input string to count the characters in
+     * @return the number of non-whitespace characters in the specified string;
+     *         returns 0 if the input string is null
      */
-
     public static int countCharacters(String str) {
+        if (str == null) {
+            return 0;
+        }
         return str.replaceAll("\\s", "").length();
     }
 }

src/test/java/com/thealgorithms/others/CountCharTest.java

@@ -2,15 +2,23 @@ package com.thealgorithms.others;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
+import org.junit.jupiter.api.DisplayName;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.CsvSource;
 
 class CountCharTest {
 
-    @Test
-    void testCountCharacters() {
-        String input = "12345";
-        int expectedValue = 5;
+    @ParameterizedTest(name = "\"{0}\" should have {1} non-whitespace characters")
+    @CsvSource({"'', 0", "'   ', 0", "'a', 1", "'abc', 3", "'a b c', 3", "'   a   b   c   ', 3", "'\tabc\n', 3", "'  a   b\tc  ', 3", "' 12345 ', 5", "'Hello, World!', 12"})
+    @DisplayName("Test countCharacters with various inputs")
+    void testCountCharacters(String input, int expected) {
+        assertEquals(expected, CountChar.countCharacters(input));
+    }
 
-        assertEquals(expectedValue, CountChar.countCharacters(input));
+    @Test
+    @DisplayName("Test countCharacters with null input")
+    void testCountCharactersNullInput() {
+        assertEquals(0, CountChar.countCharacters(null));
     }
 }