Added generateFibonacci function with 3 unit tests

fibonacci.js

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+// fibonacci.js
+/**
+ * Generates a Fibonacci sequence up to the given number of terms.
+ * @param {number} n - Number of terms to generate (must be ≥ 1)
+ * @returns {number[]} An array containing the Fibonacci sequence.
+ */
+function generateFibonacci(n) {
+  // Validate the input: must be a positive integer (no strings, decimals, or negatives)
+    if (typeof n !== 'number' || n <= 0 || !Number.isInteger(n)) {
+      throw new Error('Input must be a positive integer');
+    }
+
+
+  // Start the sequence with the first Fibonacci number
+    const sequence = [0];
+
+    // If user only wants 1 term, return [0]
+    if (n === 1) return sequence;
+
+    // Add the second Fibonacci number (1)
+    sequence.push(1);
+
+    // Generate the rest of the sequence from index 2 up to n
+    for (let i = 2; i < n; i++) {
+
+      // Each number is the sum of the two before it
+      const next = sequence[i - 1] + sequence[i - 2];
+      sequence.push(next);
+    }
+    return sequence;
+  }
+
+  module.exports = generateFibonacci;
+

fibonacci.test.js

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+// fibonacci.test.js
+const generateFibonacci = require('./fibonacci');
+
+test('generates the first 5 Fibonacci numbers', () => {
+  expect(generateFibonacci(5)).toEqual([0, 1, 1, 2, 3]);
+});
+
+test('returns only [0] for n = 1', () => {
+  expect(generateFibonacci(1)).toEqual([0]);
+});
+
+test('throws an error for non-integer input', () => {
+  expect(() => generateFibonacci('five')).toThrow('Input must be a positive integer');
+});