As a Software Engineer at Quest Diagnostics, you will play a crucial role in developing and maintaining software solutions that drive the company's core mission of improving healthcare through diagnostic testing. This role is pivotal, as the software you create directly impacts the efficiency and accuracy of diagnostic services, ultimately affecting patient outcomes. You will be part of a dynamic team that works on innovative projects involving data management, electronic health records, and integration of cutting-edge technologies. In this position, you will be involved in various aspects of the software development lifecycle, from requirements gathering to deployment and maintenance. The complexity of the projects you will encounter at Quest Diagnostics will challenge you to think critically and creatively, ensuring that you contribute to high-quality, scalable software solutions. You will have the opportunity to work with cross-functional teams, including product managers, quality assurance, and IT operations, thereby enhancing your collaborative skills and broadening your understanding of the healthcare technology landscape.
Phone Screening
reportedInitial call to assess candidate's background and fit for the role.
What to demonstrate
- Initial call to assess candidate's background and fit for the role
- Depth in Java
How to prepare
- Be able to walk your CV end to end in two minutes, and say why this company specifically.
- Have your salary expectations, notice period and location constraints ready, and ask for the rest of the loop in writing.
Technical Assessments
reportedCandidates undergo technical evaluations to demonstrate coding abilities.
What to demonstrate
- Candidates undergo technical evaluations to demonstrate coding abilities
- Depth in Java
How to prepare
- Answer aloud and timed: Describe the differences between a Primary Key and a Unique Key in a database.
- Answer aloud and timed: How do you secure a REST API?
Onsite Interview
reportedIn-person interviews that may include multiple rounds focusing on technical and behavioral aspects.
What to demonstrate
- In-person interviews that may include multiple rounds focusing on technical and behavioral aspects
- Depth in Java
How to prepare
- Answer aloud and timed: What are the concepts of Inversion of Control (IoC) and Dependency Injection (DI) in Spring?
- Answer aloud and timed: How would you approach optimizing a slow SQL query?
PracHub editorial advice for the preparation topics above.
Research the Company
Understand Quest Diagnostics' mission, values, and recent developments in healthcare technology. This knowledge will enhance your responses during interviews.
Practice Coding
Regularly solve coding challenges on platforms like LeetCode or HackerRank to sharpen your problem-solving skills.
Prepare for Behavioral Questions
Reflect on past experiences and prepare structured answers using the STAR method (Situation, Task, Action, Result) to articulate your responses effectively.
Understand the Role
Clearly define how your skills and experiences align with the responsibilities of a Software Engineer at Quest Diagnostics.
Choose a category, try a prompt, then open its approach, worked solution or follow-up when you need it.
Can you explain how memory management works in Java?
Can you explain how memory management works in Java?
Approach
- Say what the runtime actually does before reasoning about the code.
- Name what is shared across threads and what owns each piece of state.
- Identify the window where an invariant is briefly untrue.
- Distinguish a value from a reference to it, and say which one you handed out.
Follow-up
- What happens if two callers reach this at the same time?
- Where could this allocate more than you expect?
Can you explain the Dutch National Flag problem and how to solve it?
Can you explain the Dutch National Flag problem and how to solve it?
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Write a function to reverse a linked list.
Write a function to reverse a linked list.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
Explain the concept of polymorphism and provide examples.
Explain the concept of polymorphism and provide examples.
Approach
- Restate the input: its shape, its size, and what is guaranteed about it.
- Name the brute-force solution and its complexity before improving on it.
- Choose the data structure from the access pattern, not from familiarity.
- State the target complexity and say which constraint rules the naive version out.
Follow-up
- How does this change if the input no longer fits in memory?
- What is the worst case, and how likely is it on real data?
How would you approach optimizing a slow SQL query?
How would you approach optimizing a slow SQL query?
Approach
- Name the grain you start from and join outward from it.
- Check whether any join is one-to-many before aggregating, or the sums inflate.
- Say which index the query would use, and what makes it unusable.
- Handle the rows that do not match: that is usually the actual question.
Follow-up
- How does the query change if that join becomes one-to-many?
- What happens to this when the table is ten times larger?
Denormalise tenant onto revisions and backfill it live
resource_revision (revision_id, resource_id, version, actor_user_id, change_kind, patch, request_id, created_at) has 400M rows and no tenant column; tenant_id lives only on resource. Two reads need it: a tenant-scoped audit feed ordered by created_at DESC, and an offboarding purge. Both join back to resource today. Justify adding tenant_id to resource_revision against those two reads, name the anomaly the copy introduces and the constraint that prevents it, then give the ordered migration for a live table taking 1.2k writes/second — the lock each step takes, how the backfill is batched, and where each step stops being reversible. PostgreSQL 16.
Approach
- Justify from the access path rather than from taste. Without the column, the audit feed either scans resource_revision by created_at and discards other tenants' rows, or resolves the tenant's resource_ids first and probes with them — both proportional to the tenant's whole history rather than to one page. With (tenant_id, created_at DESC, revision_id DESC) it is a seek that stops at 50 rows, and the purge becomes a ranged delete instead of a join.
- Name the cost exactly: a second copy of a fact can disagree with the first. Make the disagreement unwritable rather than documented — add UNIQUE (resource_id, tenant_id) on resource so it can serve as a foreign-key target, then FOREIGN KEY (resource_id, tenant_id) REFERENCES resource (resource_id, tenant_id) on the revision table. A revision can then only ever carry its parent's tenant.
- Step one, expand: ALTER TABLE resource_revision ADD COLUMN tenant_id BIGINT NULL, with no default, so it is a catalogue change and no rewrite. It still needs ACCESS EXCLUSIVE for an instant, and that instant queues behind the longest open transaction on the table while every later query queues behind it — set lock_timeout to 2s and retry rather than wait.
- Step two, dual-write: deploy the writer that populates tenant_id on every new revision while reads still use the join. Reversible by redeploying the previous build, because nothing reads the column yet.
Follow-up
- The backfill is half finished and a rollback is required. What state is the table in, and what does the previous build do with a half-populated column?
- How do you verify the backfill actually finished, given rows are still being inserted while it runs?
What are the main features of Java 8 that you have utilized?
What are the main features of Java 8 that you have utilized?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe the differences between a Primary Key and a Unique Key in a database.
Describe the differences between a Primary Key and a Unique Key in a database.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
How do you secure a REST API?
How do you secure a REST API?
Approach
- Say who the caller is and what they do when the call fails halfway.
- Define the identity of a request so a retry cannot double-apply it.
- Separate accepted, pending, failed and confirmed; they are different facts.
- Design the error taxonomy before the success shape; callers branch on it.
Follow-up
- What happens if the caller retries after a timeout?
- How does a client discover it is on an old version of this contract?
What are the concepts of Inversion of Control (IoC) and Dependency Injection (DI) in Spring?
What are the concepts of Inversion of Control (IoC) and Dependency Injection (DI) in Spring?
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Describe how you would handle a situation where a critical bug is found in production.
Describe how you would handle a situation where a critical bug is found in production.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Provide an example of a complex problem you solved in a previous project.
Provide an example of a complex problem you solved in a previous project.
Approach
- Clarify what is being asked and what a complete answer contains.
- State your assumptions explicitly before working the problem.
- Say what you would check first and why it is the highest-information step.
- Work from the requirement backwards to the design.
Follow-up
- What assumption would you test first?
- How would you know your answer was wrong?
Exports duplicate a row range about once a week
Roughly once a week an export writes a file containing a duplicated range of rows. The affected job_run rows show attempt = 1, status = succeeded, one started_at, and a lease_owner naming a different host from the one whose logs show the job starting. Leases last 30 seconds and are heartbeated every 10 from inside the handler; lease_expires_at is computed on the worker and compared against the database's now(). Find the mechanism, and give a fix that holds even if you cannot fix the clocks.
Approach
- Start from the fact that eliminates the obvious answer. attempt = 1 means no retry was recorded, so this is not a re-run after failure; two workers ran the same row concurrently and the takeover path never touched the counter. lease_owner naming a host other than the one that started the job is the same statement from the other side.
- Enumerate the mechanisms that cause a premature takeover, then find the signal that separates them. Either the lease genuinely expired because the heartbeat did not fire, which is what happens when the heartbeat runs on the handler's own thread and the handler makes a long blocking call, or it only appeared expired because two clocks disagree, since lease_expires_at is written from the worker's clock and evaluated against the database's. The discriminator is the distribution: incidents clustered on the longest exports indict the heartbeat, incidents clustered on one host indict skew. Measure both, and measure each host's offset against the database directly.
- Read the reclaim query precisely. In PostgreSQL now() is transaction start time, not statement time, so a reclaimer holding a long transaction compares against an older timestamp than expected; clock_timestamp() is the statement-time function. This is worth ruling in or out before you redesign anything, because it changes which rows look expired.
- Remove the second clock rather than trying to synchronise it. Issue and extend the lease in the database, with lease_expires_at = now() + interval '30 seconds' in both the claim and the heartbeat, so exactly one clock is ever compared and worker skew stops mattering to this predicate.
Follow-up
- The displaced worker has already streamed half the file to object storage. What makes that side effect safe to repeat?
- You now count takeovers. What alert fires on that counter, and at what threshold?
Built from the rounds and topics Quest Diagnostics candidates report.
Prepare, practise & reflect
One practical outcome each day. Spend longer where you need it.
0 / 7 done01Map the Quest Diagnostics loop
- Write out the reported sequence: Phone Screening, Technical Assessments, Onsite Interview.
- For each round, write one sentence on what it is judging, from the description above, and mark the one you are least ready for.
Deliverable: A one-page map of the 3 reported rounds, with the weakest marked.
02Work Java
- Spend the session on Java, which Quest Diagnostics candidates report being tested on.
- Write one worked example in Java and time yourself on it.
Deliverable: One timed worked example in Java.
03Work DSA (Data Structures and Algorithms)
- Spend the session on DSA (Data Structures and Algorithms), which Quest Diagnostics candidates report being tested on.
- Write one worked example in DSA (Data Structures and Algorithms) and time yourself on it.
Deliverable: One timed worked example in DSA (Data Structures and Algorithms).
04Work Java 8 Features
- Spend the session on Java 8 Features, which Quest Diagnostics candidates report being tested on.
- Write one worked example in Java 8 Features and time yourself on it.
Deliverable: One timed worked example in Java 8 Features.
05Answer out loud: Technical / Domain Questions
- Answer aloud, timed: What are the main features of Java 8 that you have utilized?
- Answer aloud, timed: Can you explain how memory management works in Java?
Deliverable: Spoken answers to 2 reported Technical / Domain Questions question(s), under time.
06Answer out loud: Problem-Solving / Case Studies
- Answer aloud, timed: How would you approach optimizing a slow SQL query?
- Answer aloud, timed: Describe how you would handle a situation where a critical bug is found in production.
Deliverable: Spoken answers to 2 reported Problem-Solving / Case Studies question(s), under time.
07Answer out loud: Behavioral / Leadership
- Answer aloud, timed: Can you describe a time when you had to work with a difficult team member?
- Answer aloud, timed: How do you prioritize tasks when working on multiple projects?
Deliverable: Spoken answers to 2 reported Behavioral / Leadership question(s), under time.
Expand any day for tasks and deliverables. Your progress is saved on this device.
Behavioural rounds judge the decision you made and what it cost.
Can you describe a time when you had to work with a difficult team member?
Can you describe a time when you had to work with a difficult team member?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
How do you prioritize tasks when working on multiple projects?
How do you prioritize tasks when working on multiple projects?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
What motivates you to perform at your best?
What motivates you to perform at your best?
Approach
- Pick a story where you made the decision, not one where you watched it.
- State the situation in two sentences and spend the rest on the reasoning.
- Give the blast radius: what could have broken, and what you measured.
- Name the disagreement and how you resolved it with evidence.
Follow-up
- What would you do differently if you ran that again?
- How did you know your change caused the improvement?
- 01
Can you describe a time when you had to work with a difficult team member?
- 02
How do you prioritize tasks when working on multiple projects?
- 03
What motivates you to perform at your best?
What is the typical interview difficulty for this role?
The interview process for the Software Engineer position is generally considered average in difficulty, but it is essential to prepare thoroughly, especially for technical assessments.
Quest Diagnostics Software Engineer candidate reports ↗How much preparation time do candidates usually need?
Candidates typically spend a few weeks preparing for interviews, focusing on coding skills, system design, and behavioral questions.
Quest Diagnostics Software Engineer candidate reports ↗What differentiates successful candidates?
Successful candidates demonstrate strong technical skills, effective communication, and a collaborative mindset. They also align with the company’s mission and values.
Quest Diagnostics Software Engineer candidate reports ↗What is the timeline from the initial screen to an offer?
The overall timeline can vary but generally takes 2-3 weeks from the initial screening to an offer, depending on the number of interview rounds.
Quest Diagnostics Software Engineer candidate reports ↗How does the company support remote work or hybrid expectations?
Quest Diagnostics has embraced flexible work arrangements, but specific policies may vary by department. It's advisable to inquire about expectations during the interview process.
Quest Diagnostics Software Engineer candidate reports ↗What topics does Quest Diagnostics test in interviews?
Quest Diagnostics interviews most often cover Behavioral Interviewing, Stakeholder Management, Professional Self-Presentation, Analytical Reasoning, and Time Management in Interviews. The exact emphasis depends on the specific role you apply for.
Quest Diagnostics Software Engineer candidate reports ↗Sources & methodology 3 sources ↗
No official company page is cited. Rounds and questions come from candidate reports and PracHub editorial material; each source shows the date it was read.
- 01Quest Diagnostics Software Engineer candidate reports ↗
Company-reported rounds, questions and FAQ.
Candidate reports · Accessed 2026-09-22 - 02PracHub Software Engineer practice ↗
PracHub practice material, not company-reported.
PracHub page · Accessed 2026-09-22 - 03PracHub preparation framework ↗
PracHub preparation guidance.
PracHub page · Accessed 2026-09-22
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