Behavioral Change Detection
Detects removed logic lines and changed method signatures that alter runtime behavior without corresponding test updates.
Why this rule exists
A line removed from production code is a behavior change. If no test changed in the same diff, either the removed line was untested (silent regression risk) or the test it broke was deleted to make CI green.
Code example
// Removes a guard clause without touching tests
- if (user is null) throw new ArgumentNullException(nameof(user));
return user.Email;// Removes the guard AND adds a test asserting the new contract
- if (user is null) throw new ArgumentNullException(nameof(user));
return user.Email;
+ // tests/UserTests.cs
+ [Fact] public void GetEmail_NullUser_Throws_NullReference() { ... }Configuration
Disable or adjust the severity of this rule in .gauntletci.json:
{
"rules": {
"GCI0003": { "enabled": true, "severity": "Block" }
}
}See Configuration for the full schema.
Related rules
Breaking Change Risk
Detects removed public APIs and changed public method signatures that may break callers.
Edge Case Handling
Detects potential null dereferences and missing validation in added code.
Pure Context Mutation
Detects assignment operators inside property getter blocks or methods decorated with [Pure], indicating unexpected side effects.
Discussed in
Why Tests Miss Bugs
Tests pass but bugs still reach production. The categories of risk that escape test suites and why a green build is not the same as safe code.
Why Code Review Misses Bugs
Code review catches style and obvious logic errors. It routinely misses behavioral drift, contract changes, and implicit assumptions.
A Formal Framework for Behavioral Change Risk
A structured taxonomy for behavioral, contract, concurrency, and side-effect risk in code diffs.
What Is Diff-Based Analysis?
Diff-based analysis evaluates only what changed in a commit. Why that scope is the right unit of risk for pre-commit checks.
Real-world evidence
Implemented in src/GauntletCI.Core/Rules/Implementations/GCI0003_*.cs.
Eric Cogen -- Founder, GauntletCI
Twenty years in .NET production. Most of those years, the bugs that hurt me were not the ones tests caught. They were the assumptions I did not know I was making: a removed guard clause, a renamed method that still did the old thing, a catch {} that turned a page into a silent dashboard lie. GauntletCI is the checklist I wish I had run before every commit. It runs the rules I learned the hard way, so you do not have to.