Change to return undefined

lib/index.js

@@ -17,14 +17,11 @@ const max = 6
  * Make sure that there is only one top-level heading in the document by
  * adjusting headings depths accordingly.
  *
- * @template {Node} Tree
- *   Node type.
- * @param {Tree} tree
+ * @param {Node} tree
  *   Tree to change.
- * @returns {Tree}
- *   Given, modified, `tree`.
+ * @returns {undefined}
+ *   Nothing.
  */
-// To do: next major: don’t return `tree`.
 export function normalizeHeadings(tree) {
   /** @type {Array<Heading>} */
   const all = []
@@ -66,6 +63,4 @@ export function normalizeHeadings(tree) {
       }
     }
   }
-
-  return tree
 }

readme.md

@@ -111,7 +111,7 @@ headings depths accordingly.
 
 ###### Returns
 
-Given, modified, `tree` ([`Node`][node]).
+Nothing (`undefined`).
 
 ## Types
 

test/index.js

@@ -36,12 +36,12 @@ test('normalizeHeadings', async function (t) {
       )
       const actual = fromMarkdown(input)
       const expected = fromMarkdown(output)
+
       normalizeHeadings(actual)
+      removePosition(actual, true)
+      removePosition(expected, true)
 
-      assert.deepEqual(
-        removePosition(actual, true),
-        removePosition(expected, true)
-      )
+      assert.deepEqual(actual, expected)
     })
   }
 })