Quality Control

Quality Control is the set of activities focused on examining specific, individual pieces of work to determine whether they meet defined requirements and standards, identifying defects or shortfalls in particular outputs so they can be corrected before that work is considered complete or released. Where Quality Assurance concerns itself with the health of the process that produces work, Quality Control concerns itself directly with the work itself, item by item, verifying outcomes rather than designing or improving the system that generates them.

The Focus of Quality Control

Examining Specific Outputs

Quality control activities are applied to a concrete, identifiable piece of work — a feature, a component, a release candidate — checking that particular item against the criteria it is expected to satisfy, rather than assessing the general practices used to build it.

Identifying Deviations From Requirements

The central purpose of quality control is to detect any gap between what a piece of work actually does and what it was supposed to do, surfacing these deviations as defects that require correction before the work can be considered acceptable.

Core Quality Control Activities

Functional Testing

Executing the work under defined conditions and comparing actual behavior against expected behavior is the most direct quality control activity, verifying that the item performs as intended across both typical and edge-case scenarios.

Non-Functional Testing

Verifying characteristics such as performance under load, security posture, and usability against defined thresholds ensures the item meets standards that go beyond simple functional correctness, which are equally part of what quality control examines.

Code and Artifact Review

Directly examining the implementation or artifact itself, whether through manual review or automated checks, identifies issues in structure, correctness, or adherence to standards that might not be visible through behavioral testing alone.

Defect Logging and Verification

Recording identified defects with sufficient detail to allow them to be understood and corrected, and subsequently verifying that a fix actually resolves the defect without introducing new problems, completes the quality control cycle for each identified issue.

Quality Control Within the Agile Workflow

Continuous Rather Than End-Stage

Rather than being concentrated in a single phase at the end of a project, Agile quality control activities occur continuously throughout each iteration, applied to items as they near or reach completion, consistent with the incremental nature of Agile delivery.

Integrated With Built In Quality

Many quality control checks in Agile teams are automated and embedded directly into the development pipeline, such as automated test suites run on every change, blending quality control with the built-in quality practices that reduce reliance on manual, end-stage inspection.

Tied to the Definition of Done

Quality control activities are frequently the specific mechanisms through which a team verifies that an item satisfies its definition of done, providing the concrete evidence needed before an item can be marked genuinely complete.

Roles Involved in Quality Control

Distributed Responsibility

Consistent with shared quality ownership, quality control activities in Agile teams are typically performed by multiple team members rather than a single isolated function, with developers, testers, and others all contributing checks relevant to their perspective on the work.

Specialized Testing Expertise

Where a team includes members with dedicated testing expertise, their quality control contribution often focuses on more complex or exploratory verification that benefits from specialized skill, complementing the broader checks performed collectively by the team.

Relationship to Quality Assurance

Quality Control Provides Evidence for Quality Assurance

The specific defects and patterns identified through quality control activity serve as the raw evidence that quality assurance uses to investigate root causes and improve the underlying process, meaning the two disciplines depend on each other despite their different focus.

Neither Substitutes for the Other

A team that performs quality control thoroughly but neglects quality assurance will continue to encounter the same categories of defects repeatedly, since the underlying process weaknesses go unaddressed, while a team that focuses only on quality assurance without quality control risks releasing specific defects that a sound process alone cannot guarantee against.

Consequences of Weak Quality Control

Defects Reaching Delivery

Without adequate quality control, defects that a more thorough check would have caught instead reach stakeholders or end users, where the cost and visibility of the failure are typically far greater than if caught earlier.

Erosion of Confidence in Completed Work

If items marked complete are later found to contain defects that quality control should have caught, trust in the team's definition of "done" itself begins to erode, undermining the reliability of status reporting across the project.

Visual Representation

An item that fails quality control is returned for correction rather than proceeding, expressed as a governing condition:

Quality Control is the discipline of testing this condition rigorously against every relevant item before it is allowed to be considered complete.