fix: guard isTestoFile against invalid VirtualFile

TestoIconProvider could trigger an "Outdated stub in index" exception
when invoked on a stale PsiFile whose underlying physical file no
longer existed (e.g. a deleted vendor/autoload.php still cached in the
stub index). isTestoFile() walked the AST via PsiTreeUtil before any
validity check, forcing AST load and crashing on the stub mismatch.

Short-circuit isTestoFile() if the file is not a PhpFile, has no
VirtualFile, or its VirtualFile is no longer valid - avoiding any PSI
traversal in those cases.

Author: claude

src/main/kotlin/com/github/xepozz/testo/mixin.kt

@@ -43,9 +43,15 @@ fun PsiElement.isTestoClass() = when (this) {
     else -> false
 }
 
-fun PsiFile.isTestoFile() = when (this) {
-    is PhpFile -> TestoTestDescriptor.isTestClassName(name.substringBeforeLast(".")) || isTestoClassFile() || isTestoFunctionFile() || isTestBenchFile() || isTestoConfigFile()
-    else -> false
+fun PsiFile.isTestoFile(): Boolean {
+    if (this !is PhpFile) return false
+    val vFile = virtualFile ?: return false
+    if (!vFile.isValid) return false
+    return TestoTestDescriptor.isTestClassName(name.substringBeforeLast("."))
+        || isTestoClassFile()
+        || isTestoFunctionFile()
+        || isTestBenchFile()
+        || isTestoConfigFile()
 }
 
 fun PhpFile.isTestoConfigFile() = PsiTreeUtil.findChildrenOfType(this, ClassReference::class.java)

src/test/kotlin/com/github/xepozz/testo/MixinPsiTest.kt

@@ -1,5 +1,6 @@
 package com.github.xepozz.testo
 
+import com.intellij.openapi.application.WriteAction
 import com.intellij.psi.util.PsiTreeUtil
 import com.intellij.testFramework.TestDataPath
 import com.intellij.testFramework.fixtures.BasePlatformTestCase
@@ -155,6 +156,24 @@ class MixinPsiTest : BasePlatformTestCase() {
         assertTrue("File containing test class should be a Testo file", psiFile.isTestoFile())
     }
 
+    fun testIsTestoFile_invalidVirtualFile_returnsFalse() {
+        val psiFile = myFixture.configureByText(
+            "DeletedTest.php",
+            """<?php class DeletedTest { public function testSomething(): void {} }"""
+        ) as PhpFile
+
+        assertTrue("Precondition: file should initially be detected as a Testo file", psiFile.isTestoFile())
+
+        val vFile = psiFile.virtualFile!!
+        WriteAction.runAndWait<Throwable> { vFile.delete(this) }
+
+        assertFalse("VirtualFile should be invalid after deletion", vFile.isValid)
+        assertFalse(
+            "isTestoFile must return false when the underlying VirtualFile is invalid",
+            psiFile.isTestoFile()
+        )
+    }
+
     // ---- isTestoExecutable ----
 
     fun testIsTestoExecutable_testMethod() {