☔ test: Add regression test for deletion of node with successor.

Author: make-github-pseudonymous-again

test/src/regression/root-is-always-black.js

@@ -0,0 +1,17 @@
+import test from 'ava';
+
+import {increasing} from '../../fixtures.js';
+import {empty} from '../../../src/index.js';
+
+test('root + succ', (t) => {
+	const tree = empty(increasing);
+	t.true(tree.isEmpty());
+	tree.add(0);
+	t.false(tree.isEmpty());
+	tree.add(1);
+	t.false(tree.isEmpty());
+	tree.remove(0);
+	t.false(tree.isEmpty());
+	tree.remove(1);
+	t.true(tree.isEmpty());
+});