test: allow compact diff for test failures (#6783)

* Allow the compact diff for tests

* Update the doc

* Update docs/pages/contribution/testing/index.md

Co-authored-by: Julien <jeluard@users.noreply.github.com>

* Fix linting on docs

* Fix linting

---------

Co-authored-by: Julien <jeluard@users.noreply.github.com>

docs/pages/contribution/testing/index.md

@@ -2,6 +2,12 @@
 
 Testing is critical to the Lodestar project and there are many types of tests that are run to build a product that is both effective AND efficient. This page will help to break down the different types of tests you will find in the Lodestar repo.
 
+There are few flags you can set through env variables to override behavior of testing and it's output.
+
+| ENV variable      | Effect | Impact                                                                                                      |
+| ----------------- | ------ | ----------------------------------------------------------------------------------------------------------- |
+| TEST_COMPACT_DIFF | All    | Will strip down the object difference rendered during test failures. Very useful for large object matching. |
+
 ### Unit Tests
 
 This is the most fundamental type of test in most code bases. In all instances mocks, stubs and other forms of isolation are used to test code on a functional, unit level. See the [Unit Tests](./unit-tests.md) page for more information.

scripts/vitest/vitest.diff.ts

@@ -0,0 +1,9 @@
+import type {DiffOptions} from "vitest";
+
+export default {
+  aIndicator: "--",
+  bIndicator: "++",
+  includeChangeCounts: true,
+  contextLines: 2,
+  expand: false,
+} satisfies DiffOptions;

vitest.base.unit.config.ts

@@ -41,5 +41,6 @@ export default defineConfig({
         "**/node_modules/**",
       ],
     },
+    diff: process.env.TEST_COMPACT_DIFF ? path.join(import.meta.dirname, "./scripts/vitest/vitest.diff.ts") : undefined,
   },
 });