Test

README.md

@@ -1,4 +1,69 @@
 # constraint-error-ci-example
-
-- example of catching constraint errors during test execution with `lldb`.
-- check the [pull request](https://github.com/kaanbiryol/constraint-error-ci-example/pull/3) to see danger errors.
+
+Catch broken Auto Layout constraints during test execution using LLDB breakpoints, and surface them as PR warnings via Danger.
+
+## Why?
+
+`UIViewAlertForUnsatisfiableConstraints` fires at runtime but is invisible in CI. Broken constraints silently ship to production, causing layout bugs that are hard to trace back to a specific change.
+
+This project demonstrates a technique to intercept these warnings during tests and block them at the PR level.
+
+## What it does
+
+- Sets an LLDB breakpoint on `UIViewAlertForUnsatisfiableConstraints` that runs in the background during test execution
+- A Python script attached to the breakpoint walks the call stack, identifies the failing `XCTestCase`, and logs it to `brokenConstraints.txt`
+- Danger reads the output file and posts constraint violations as warnings on the pull request
+- See [PR #3](https://github.com/kaanbiryol/constraint-error-ci-example/pull/3) for an example of the Danger output
+
+## Requirements
+
+- Xcode 14.1+
+- macOS (CI runs on `macos-latest`)
+- `danger-swift` (installed via Homebrew in CI)
+
+## Quick start
+
+```bash
+# Run tests locally
+make test
+
+# Run LLDB constraint detection (background) + tests
+lldb --source lldb-command &
+make test
+```
+
+## How it works
+
+1. **LLDB attaches** to the test process and sets a breakpoint on `UIViewAlertForUnsatisfiableConstraints` with auto-continue enabled
+2. **On each hit**, a Python command iterates the thread's frames, finds the `XCTestCase` subclass, and appends the module/file/function to `brokenConstraints.txt`
+3. **After tests complete**, Danger checks for the output file and warns on the PR with the logged violations
+
+## CI pipeline
+
+Defined in `.github/workflows/snapshot.yml`, triggered on pull requests:
+
+```
+checkout -> lldb --source lldb-command & -> make test -> danger-swift ci
+```
+
+## Project structure
+
+```
+lldb-command          # LLDB breakpoint script (Python)
+Dangerfile.swift      # Danger config - reads constraint errors, warns on PR
+Makefile              # xcodebuild wrapper
+constraint-error-ci-example/
+  BrokenView.swift    # UIView with intentionally broken constraints (demo)
+constraint-error-ci-snapshots/
+  BrokenViewTests.swift  # Snapshot tests that trigger constraint violations
+```
+
+## Limitations
+
+- LLDB must attach to the process before tests start - requires background launch (`&`)
+- The `lldb-command` script relies on `GITHUB_WORKSPACE` env var, so local runs won't write to `brokenConstraints.txt` without modification
+- Only detects constraints broken during test execution - no static analysis
+
+## License
+
+MIT

constraint-error-ci-snapshots/BrokenViewTests.swift

@@ -12,22 +12,22 @@ import SnapshotTesting
 
 final class BrokenViewTests: XCTestCase {
 
-//    func testBrokenView0() {
-//        let brokenView = BrokenView()
-//        brokenView.text = "BrokenView0"
-//        assertSnapshots(matching: brokenView, as: [.image])
-//    }
-//    
-//    func testBrokenView1() {
-//        let brokenView = BrokenView()
-//        brokenView.text = "BrokenView1"
-//        assertSnapshots(matching: brokenView, as: [.image])
-//    }
-//    
-//    func testPassingTest() {
-//        let brokenView = UILabel()
-//        brokenView.text = "BrokenView2"
-//        assertSnapshots(matching: brokenView, as: [.image])
-//    }
+    func testBrokenView0() {
+        let brokenView = BrokenView()
+        brokenView.text = "BrokenView0"
+        assertSnapshots(matching: brokenView, as: [.image])
+    }
+
+    func testBrokenView1() {
+        let brokenView = BrokenView()
+        brokenView.text = "BrokenView1"
+        assertSnapshots(matching: brokenView, as: [.image])
+    }
+
+    func testPassingTest() {
+        let brokenView = UILabel()
+        brokenView.text = "BrokenView2"
+        assertSnapshots(matching: brokenView, as: [.image])
+    }
 
 }