Add tests for completions crash (#53472)

tests/cases/fourslash/server/completionsOverridingMethodCrash2.ts

@@ -0,0 +1,69 @@
+/// <reference path="../fourslash.ts" />
+
+// @Filename: /tsconfig.json
+//// {
+////   "compilerOptions": {
+////     "module": "nodenext"
+////   }
+//// }
+
+// @Filename: /utils.ts
+//// export class Element {
+////     // ...
+//// }
+//// 
+//// export abstract class Component {
+////     abstract render(): Element;
+//// }
+
+// @Filename: /classes.ts
+//// import { Component } from "./utils.js";
+//// 
+//// export class MyComponent extends Component {
+////     render/**/
+//// }
+
+goTo.marker("");
+verify.completions({
+    marker: "",
+    isNewIdentifierLocation: true,
+    preferences: {
+        includeCompletionsWithInsertText: true,
+        includeCompletionsWithSnippetText: true,
+        includeCompletionsWithClassMemberSnippets: true,
+    },
+    includes: [
+        {
+            name: "render",
+            sortText: completion.SortText.ClassMemberSnippets,
+            isSnippet: true,
+            insertText: "render(): Element {\r\n    $0\r\n}",
+            hasAction: true,
+            source: completion.CompletionSource.ClassMemberSnippet,
+        }
+    ]
+});
+
+goTo.file("/utils.ts");
+goTo.marker("");
+edit.backspace();
+
+verify.completions({
+    marker: "",
+    isNewIdentifierLocation: true,
+    preferences: {
+        includeCompletionsWithInsertText: true,
+        includeCompletionsWithSnippetText: true,
+        includeCompletionsWithClassMemberSnippets: true,
+    },
+    includes: [
+        {
+            name: "render",
+            sortText: completion.SortText.ClassMemberSnippets,
+            isSnippet: true,
+            insertText: "render(): Element {\r\n    $0\r\n}",
+            hasAction: true,
+            source: completion.CompletionSource.ClassMemberSnippet,
+        }
+    ]
+});