test: add tests for --test-inspect-depth

Author: Jia-ben00

test/parallel/test-test-runner-inspect-depth.js

@@ -0,0 +1,49 @@
+'use strict';
+
+// This test verifies that the --test-inspect-depth CLI option controls
+// the depth of util.inspect() used when formatting errors in test reporters.
+
+const { spawnSync } = require('node:child_process');
+const { assertIncludes } = require('../common');
+const { writeFileSync, mkdtempSync } = require('node:fs');
+const { tmpdir } = require('node:os');
+const { join } = require('node:path');
+
+const tmp = mkdtempSync(join(tmpdir(), 'node-test-inspect-depth-'));
+
+// Create a test file that throws an error with a deeply nested object.
+const testFile = join(tmp, 'test.js');
+writeFileSync(testFile, `
+const test = require('node:test');
+
+test('nested error', () => {
+  const err = new Error('fail');
+  err.data = { level1: { level2: { level3: { level4: { value: 42 } } } } };
+  throw err;
+});
+`);
+
+// Run without --test-inspect-depth (default depth = 2, level3+ should be [Object])
+{
+  const result = spawnSync(process.execPath, ['--test', testFile], {
+    encoding: 'utf8',
+  });
+  assertIncludes(result.stderr + result.stdout, '[Object]');
+}
+
+// Run with --test-inspect-depth=10 (all levels should be expanded)
+{
+  const result = spawnSync(process.execPath, ['--test', '--test-inspect-depth=10', testFile], {
+    encoding: 'utf8',
+  });
+  assertIncludes(result.stderr + result.stdout, 'level4');
+  assertIncludes(result.stderr + result.stdout, 'value: 42');
+}
+
+// Run with --test-inspect-depth=0 (no expansion, all objects [Object])
+{
+  const result = spawnSync(process.execPath, ['--test', '--test-inspect-depth=0', testFile], {
+    encoding: 'utf8',
+  });
+  assertIncludes(result.stderr + result.stdout, '[Object]');
+}