To succeed in the Costar interview process, you must demonstrate a balanced blend of strong technical capabilities, structured problem-solving, and clear communication.

Database & SQL Proficiency – You must be highly comfortable writing and explaining SQL queries on the fly. Interviewers assess your ability to manipulate data, join tables, and validate complex data schemas. You can demonstrate strength here by explaining your query logic step-by-step as you write it.

Platform-Specific Diagnostics – Whether you are testing web platforms or mobile apps, you need to understand the underlying architecture. For mobile roles, this means knowing how to use ADB commands, extract device logs, and locate app identifiers. For web roles, it means demonstrating a deep familiarity with DOM manipulation, network payloads, and browser performance.

Structured Test Design – Interviewers look at how you break down complex systems into testable components. You should approach test scenarios systematically, covering positive paths, negative paths, boundary conditions, and edge cases. Always explain the "why" behind your testing strategy.

Collaboration & Adaptability – At Costar, QA is a highly collaborative function. You will interact with developers, product managers, and engineering directors. You must show that you can communicate bugs clearly, advocate for quality without causing friction, and adapt when project requirements change suddenly.

The interview process for a QA Engineer at Costar is highly structured, typically consisting of three main stages designed to evaluate your cultural fit, technical competence, and practical problem-solving abilities. The process is rigorous and requires a significant time investment, often culminating in a comprehensive onsite panel.

The journey begins with an initial recruiter screen, followed by a deeper technical evaluation with QA managers and team leads. If you pass these initial screens, you will be invited to a multi-hour onsite interview. This onsite loop is highly collaborative, giving you the opportunity to interact directly with future team members, a dedicated SQL lead, and engineering directors.

The visual timeline above outlines the typical progression of the Costar QA interview loop. Candidates should use this timeline to pace their preparation, focusing first on high-level testing concepts and behavioral alignment, before diving deep into SQL exercises and platform-specific technical diagnostics ahead of the onsite panel. While the exact duration of the onsite can vary, you should prepare for a comprehensive, half-day experience that tests both your hard technical skills and your situational judgment.

SQL & Data Validation

Data accuracy is the cornerstone of Costar products. The SQL evaluation is often conducted by a dedicated SQL lead or database specialist who will assess your ability to write clean, optimized queries under pressure.

Be ready to go over:

• Complex Joins – Combining data from multiple tables using inner, outer, self, and cross joins.
• Data Aggregation – Utilizing GROUP BY, HAVING, and aggregate functions to analyze data distributions.
• Subqueries & CTEs – Writing nested queries and Common Table Expressions to solve complex data retrieval challenges.
• Advanced concepts (less common) – Database indexing, performance tuning of slow-running queries, and stored procedure validation.

Example questions or scenarios:

• "Given a schema with properties, agents, and transactions, write a query to find the top three agents by transaction volume in a specific zip code."
• "How would you write a test script to automatically compare a source database table with a target table after a nightly ETL job run?"

Web & Mobile QA Diagnostics

Costar platforms span web portals and native mobile applications. You must demonstrate a strong command of the diagnostic tools and commands required to troubleshoot issues on these platforms.

Be ready to go over:

• ADB and Fastboot – Utilizing ADB commands to install builds, capture screenshots, clear app data, and extract system logs.
• App Identifiers – Locating and utilizing bundle IDs and package names for automation configurations and manual testing.
• API and Network Sniffing – Inspecting HTTP requests, response payloads, and headers using proxy tools or browser inspector networks.
• Advanced concepts (less common) – Simulating poor network conditions, testing battery drain/resource usage on mobile devices, and memory leak analysis.

Example questions or scenarios:

• "Walk me through the exact ADB commands you would run to pull a crash log from an Android device connected to your workstation."
• "If a web page is loading slowly, how do you use browser developer tools to isolate whether the bottleneck is in the frontend rendering or the backend API response?"

Test Automation & Framework Design

Automation is key to maintaining deployment velocity at Costar. You will be evaluated on your ability to write maintainable test code and your understanding of modern test automation patterns.

Be ready to go over:

• Page Object Model (POM) – Designing scalable and maintainable UI automation suites.
• Handling Asynchronous Behavior – Implementing smart waits, explicit waits, and fluent waits rather than hardcoded sleep statements.
• API Automation – Writing automated tests to validate RESTful API endpoints, payloads, status codes, and response times.
• Advanced concepts (less common) – Parallel test execution, configuring headless test runs in Docker containers, and custom test reporting libraries.

Example questions or scenarios:

• "How would you design an automated test suite to validate a complex, multi-step checkout checkout process on a web application?"
• "What is your strategy for managing test data state before and after automated test runs?"

As a QA Engineer at Costar, your daily activities will extend far beyond basic manual execution. You will be embedded within an agile development team, actively participating in sprint planning, grooming sessions, and retrospective meetings. Your primary objective is to build quality into the product lifecycle from the very beginning.

You will spend a significant portion of your time designing, writing, and executing test strategies. This includes writing automated test scripts for UI and API layers, performing manual exploratory testing on new features, and validating backend data migrations. You will also be responsible for maintaining and expanding existing automation frameworks to support continuous integration.

Collaboration is a daily priority. You will work side-by-side with software engineers to reproduce complex defects, partner with product managers to clarify acceptance criteria, and align with database administrators to ensure data integrity. When critical issues arise, you will act as a key advisor, helping the team assess risks and make informed release decisions.