Selenium vs Flask: Comparison for Beginners 2026

# Selenium — a realistic login test
# (the kind of script you write as a QA automation engineer)

from selenium import webdriver
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
import pytest

@pytest.fixture
def browser():
    driver = webdriver.Chrome()
    driver.implicitly_wait(5)
    yield driver
    driver.quit()

def test_login_success(browser):
    browser.get("https://example.com/login")

    # Find elements and interact
    browser.find_element(By.ID, "email").send_keys("user@example.com")
    browser.find_element(By.ID, "password").send_keys("pass123")
    browser.find_element(By.XPATH, "//button[text()='Log in']").click()

    # Wait for dashboard to appear
    WebDriverWait(browser, 10).until(
        EC.presence_of_element_located((By.CLASS_NAME, "dashboard"))
    )

    assert "dashboard" in browser.current_url
    assert browser.find_element(By.CSS_SELECTOR, ".welcome-msg").is_displayed()

def test_login_invalid_credentials(browser):
    browser.get("https://example.com/login")
    browser.find_element(By.ID, "email").send_keys("bad@example.com")
    browser.find_element(By.ID, "password").send_keys("wrong")
    browser.find_element(By.XPATH, "//button[text()='Log in']").click()

    error = WebDriverWait(browser, 10).until(
        EC.presence_of_element_located((By.CLASS_NAME, "error-msg"))
    )
    assert "invalid" in error.text.lower()

# Skills demonstrated: WebDriver, waits, Pytest, assertions, test design.

# Flask — a realistic user API
# (the kind of app you build as a backend developer)

from flask import Flask, request, jsonify
from flask_sqlalchemy import SQLAlchemy
from werkzeug.security import generate_password_hash, check_password_hash

app = Flask(__name__)
app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite:///users.db"
app.config["SQLALCHEMY_TRACK_MODIFICATIONS"] = False
db = SQLAlchemy(app)

class User(db.Model):
    id = db.Column(db.Integer, primary_key=True)
    email = db.Column(db.String(120), unique=True, nullable=False)
    password_hash = db.Column(db.String(200), nullable=False)

@app.route("/api/register", methods=["POST"])
def register():
    data = request.get_json()

    if not data or not data.get("email") or not data.get("password"):
        return jsonify({"error": "Email and password required"}), 400

    if User.query.filter_by(email=data["email"]).first():
        return jsonify({"error": "Email already registered"}), 409

    user = User(
        email=data["email"],
        password_hash=generate_password_hash(data["password"]),
    )
    db.session.add(user)
    db.session.commit()

    return jsonify({"id": user.id, "email": user.email}), 201

@app.route("/api/login", methods=["POST"])
def login():
    data = request.get_json()
    user = User.query.filter_by(email=data["email"]).first()

    if not user or not check_password_hash(user.password_hash, data["password"]):
        return jsonify({"error": "Invalid credentials"}), 401

    return jsonify({"message": "Login successful", "user_id": user.id})

if __name__ == "__main__":
    with app.app_context():
        db.create_all()
    app.run(debug=True)

# Skills demonstrated: Flask, SQLAlchemy, password hashing, validation.