fix source mapping in tests (#1891)

Author: matthewbastien

package-lock.json

@@ -2035,6 +2035,7 @@
     "@types/semver": "^7.7.1",
     "@types/sinon": "^17.0.4",
     "@types/sinon-chai": "^3.2.12",
+    "@types/source-map-support": "^0.5.10",
     "@types/svg2ttf": "^5.0.3",
     "@types/svgicons2svgfont": "^10.0.5",
     "@types/ttf2woff": "^2.0.4",

package.json

@@ -11,19 +11,34 @@
 // SPDX-License-Identifier: Apache-2.0
 //
 //===----------------------------------------------------------------------===//
-// Use source-map-support to get better stack traces
-import "source-map-support/register";
-
 import * as chai from "chai";
 import * as chaiAsPromised from "chai-as-promised";
 import * as chaiSubset from "chai-subset";
 import * as fs from "fs";
+import * as mockFS from "mock-fs";
 import * as path from "path";
 import * as sinonChai from "sinon-chai";
+import * as sourceMapSupport from "source-map-support";
 import * as tsConfigPaths from "tsconfig-paths";
 
 import { installTagSupport } from "./tags";
 
+// Use source-map-support to get better stack traces.
+//
+// We have to override retrieveFile() here because any test that uses mock-fs will break
+// source map lookups. This will make sure that, even if mock-fs is in effect, source map
+// support can still find the files that it needs to.
+sourceMapSupport.install({
+    retrieveFile(path: string): string | null {
+        return mockFS.bypass(() => {
+            if (!fs.existsSync(path)) {
+                return null;
+            }
+            return fs.readFileSync(path, "utf-8");
+        });
+    },
+});
+
 const tsConfig = JSON.parse(
     // __dirname points to dist/test when transpiled, but we need the tsconfig.json in the real test/
     fs.readFileSync(path.join(__dirname, "../../test/tsconfig.json"), "utf-8")