Implement countChar and add Jest tests using TDD

Author: remimarcelle

Sprint-3/2-practice-tdd/count.js

@@ -1,5 +1,22 @@
+/**
+ * Counts how many times a single character appears in a string.
+ *
+ * @param {string} stringOfCharacters - The string to search through.
+ * @param {string} findCharacter - The single character to count.
+ * @returns {number} The number of times findCharacter appears in stringOfCharacters.
+ *
+ * @see https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/for...of
+ */
+
 function countChar(stringOfCharacters, findCharacter) {
-  return 5
+  let count = 0;
+  for (const char of stringOfCharacters) {
+    if (char === findCharacter) {
+      count++; // this means count = count + 1. This term is called 
+      // "incrementing" the count variable.
+    }
+  }
+  return count;
 }
 
 module.exports = countChar;

Sprint-3/2-practice-tdd/count.test.js

@@ -22,3 +22,20 @@ test("should count multiple occurrences of a character", () => {
 // And a character `char` that does not exist within `str`.
 // When the function is called with these inputs,
 // Then it should return 0, indicating that no occurrences of `char` were found.
+
+// test for Scenario "No Occurrences" — char isn't in the string, expect 0
+test("should return 0 when the character is not found", () => {
+  const str = "fiendish";
+  const char = "a";
+  const count = countChar(str, char);
+  expect(count).toEqual(0);
+});
+
+// extra edge case — counts 's' in "Mississippi" (should be 4)
+// Good real-world style input to make sure the loop works across a longer string.
+test("should count occurrences correctly in a mixed string", () => {
+  const str = "Apple";
+  const char = "p";
+  const count = countChar(str, char);
+  expect(count).toEqual(2);
+});