test: improve util-format code coverage

Add test case for calling `util.format()` with a BigInt and a separator. Refs: https://coverage.nodejs.org/coverage-986cf3b986c6c3e1/lib/internal/util/inspect.js.html#L2042 PR-URL: nodejs#41572 Reviewed-By: Tobias Nießen <[email protected]> Reviewed-By: Mestery <[email protected]> Reviewed-By: Luigi Pinca <[email protected]> Reviewed-By: James M Snell <[email protected]> Reviewed-By: Mohammed Keyvanzadeh <[email protected]> Reviewed-By: Zeyu Yang <[email protected]>

Author: Trott

test/parallel/test-util-format.js

@@ -143,6 +143,13 @@ assert.strictEqual(
 '1180591620717411303424n 12345678901234567890123n'
 );
 
+assert.strictEqual(
+util.formatWithOptions(
+{numericSeparator: true},
+'%i %d',1180591620717411303424n,12345678901234567890123n),
+'1_180_591_620_717_411_303_424n 12_345_678_901_234_567_890_123n'
+);
+
 // Float format specifier
 assert.strictEqual(util.format('%f'),'%f');
 assert.strictEqual(util.format('%f',42.0),'42');