test(resume-parser): add error-resilience test suite (JhaSourav07#2878) (JhaSourav07#3003)

## Description

Adds the comprehensive `resume-parser.error-resilience.test.ts` test
suite to cover exception safety, null/undefined checks, corrupt binary
data fallbacks, buffer conversion failures, malformed structures, and
regexp backtracking boundary limits.

Fixes JhaSourav07#2878

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## Visual Preview

N/A (Utility/Unit Tests only)

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- [x] I have read the `CONTRIBUTING.md` file.
- [x] I have tested these changes locally.
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resolved all errors.
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parameter.
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Author: JhaSourav07

lib/resume-parser.error-resilience.test.ts

@@ -0,0 +1,108 @@
+import { describe, it, expect, vi } from 'vitest';
+import { parseResume } from './resume-parser';
+
+describe('resume-parser-error-resilience', () => {
+  it('should handle non-printable characters gracefully by replacing them and parsing the remaining text', async () => {
+    // \x00 is non-printable. It should be replaced with a space.
+    const text = 'John Doe\n\x00\x01\x02john.doe@example.com\nSkills\nJavaScript, Python';
+    const buffer = Buffer.from(text);
+    const result = await parseResume(buffer, 'application/pdf');
+
+    expect(result.name).toBe('John Doe');
+    expect(result.email).toBe('john.doe@example.com');
+    expect(result.skills).toContain('JavaScript');
+    expect(result.skills).toContain('Python');
+  });
+
+  it('should throw an error/TypeError if the buffer is null or undefined (exception safety)', async () => {
+    // Ensure that passing invalid parameters rejects or throws a TypeError rather than hanging
+    await expect(parseResume(null as unknown as Buffer, 'application/pdf')).rejects.toThrow();
+    await expect(parseResume(undefined as unknown as Buffer, 'application/pdf')).rejects.toThrow();
+  });
+
+  it('should not throw and handle corrupt/binary buffers by returning empty fields', async () => {
+    // Binary/corrupt data that doesn't resemble a text resume
+    const binaryData = Buffer.from([
+      0x89, 0x50, 0x4e, 0x47, 0x0d, 0x0a, 0x1a, 0x0a, 0x00, 0x00, 0x00,
+    ]);
+    const result = await parseResume(binaryData, 'application/pdf');
+
+    expect(result).toEqual({
+      name: '',
+      email: '',
+      phone: '',
+      skills: [],
+      education: [],
+      experience: [],
+    });
+  });
+
+  it('should handle buffer toString failures gracefully (exception safety)', async () => {
+    const mockBuffer = Buffer.from('Some text');
+    vi.spyOn(mockBuffer, 'toString').mockImplementation(() => {
+      throw new Error('Buffer conversion failed');
+    });
+
+    await expect(parseResume(mockBuffer, 'application/pdf')).rejects.toThrow(
+      'Buffer conversion failed'
+    );
+    vi.restoreAllMocks();
+  });
+
+  it('should skip malformed education entries (e.g. invalid date ranges) instead of throwing', async () => {
+    const text = `John Doe
+Education
+University of Toronto 201-202
+Harvard College 2020 to invalid
+MIT 2015 to 2019
+`;
+    const buffer = Buffer.from(text);
+    const result = await parseResume(buffer, 'application/pdf');
+
+    expect(result.education).toEqual([
+      {
+        institution: 'MIT 2015 to 2019',
+        degree: '',
+        field: '',
+        startDate: '2015',
+        endDate: '2019',
+      },
+    ]);
+  });
+
+  it('should skip malformed experience entries instead of throwing', async () => {
+    const text = `John Doe
+Experience
+Software Developer at Google (no date)
+Intern at Apple 202 to present
+Senior Engineer at Meta 2018 - 2021
+`;
+    const buffer = Buffer.from(text);
+    const result = await parseResume(buffer, 'application/pdf');
+
+    expect(result.experience).toEqual([
+      {
+        company: 'Senior Engineer at Meta 2018 - 2021',
+        role: '',
+        startDate: '2018',
+        endDate: '2021',
+        description: '',
+      },
+    ]);
+  });
+
+  it('should handle extremely long single-word inputs without causing RegExp backtracking or crashing', async () => {
+    const longWord = 'A'.repeat(10000);
+    const text = `John Doe\n${longWord}@example.com\nSkills\n${longWord}`;
+    const buffer = Buffer.from(text);
+
+    const startTime = Date.now();
+    const result = await parseResume(buffer, 'application/pdf');
+    const duration = Date.now() - startTime;
+
+    // Check that it didn't hang (completed within 500ms)
+    expect(duration).toBeLessThan(500);
+    expect(result.name).toBe('John Doe');
+    expect(result.email).toContain('@example.com');
+  });
+});