484: Add warning about Psalm baseline to readme + functional test

README.md

@@ -25,6 +25,11 @@
 vendor/bin/roave-infection-static-analysis-plugin
 ```
 
+Do not use this tool if your project has a 
+[Psalm baseline](https://psalm.dev/docs/running_psalm/dealing_with_code_issues/#using-a-baseline-file) file. In that
+case issues that are ignored due to being present in the baseline will be reported as killed, spuriously inflating your 
+mutation score indicator. See [issue #484](https://github.com/Roave/infection-static-analysis-plugin/issues/484).
+
 ### Configuration
 
 The `roave-infection-static-analysis-plugin` binary accepts all of `infection` flags and arguments, and an additional `--psalm-config` argument.

test/asset/ProjectWithPsalmBaseline/.gitignore

@@ -0,0 +1 @@
+.phpunit.cache

test/asset/ProjectWithPsalmBaseline/composer.json

@@ -0,0 +1,25 @@
+{
+    "name": "acme/project-with-psalm-baseline",
+    "description": "Example hellow world app that uses a Psalm baseline",
+    "type": "project",
+    "autoload": {
+        "psr-4": {
+            "Acme\\ProjectWithPsalmBaseline\\": "src/"
+        }
+
+    },
+    "_comment": "Depending on the published version of ISAP is not great here, we should be testing against the version that exists locally. I had trouble getting that to work.",
+    "require-dev": {
+        "vimeo/psalm": "^5.16",
+        "phpunit/phpunit": "^10.5.1",
+        "roave/infection-static-analysis-plugin": "*"
+    },
+    "config": {
+        "platform": {
+            "php": "8.1.99"
+        },
+        "allow-plugins": {
+            "infection/extension-installer": true
+        }
+    }
+}