Answer product-owner round 1: name the cycle in its own message and in the error table

src/adf/document.test.ts

@@ -83,18 +83,18 @@ test("reads a node's siblings as a walk rather than as one call's arguments", ()
   assert.equal(fault(wide), 'accepted')
 })
 
-test('refuses a document that holds itself, and accepts one sharing a node or a mark', () => {
-  const notANode = "an ADF document's content holds ADF nodes: one of them is not"
+test('refuses a node or an attribute value holding itself, and accepts one shared', () => {
+  const holdsItself = 'an ADF document is a tree: a node or an attribute value holds itself'
   const paragraph: { content: unknown[]; type: string } = { content: [], type: 'paragraph' }
   paragraph.content.push(paragraph)
-  assert.equal(fault({ content: [paragraph], type: 'doc', version: 1 }), notANode)
+  assert.equal(fault({ content: [paragraph], type: 'doc', version: 1 }), holdsItself)
   const document: { content: unknown[]; type: string; version: number } = { content: [], type: 'doc', version: 1 }
   document.content.push(document)
-  assert.equal(fault(document), notANode)
+  assert.equal(fault(document), holdsItself)
   const attrs: Record<string, unknown> = {}
   attrs['a'] = [attrs]
-  assert.equal(fault({ content: [{ attrs, type: 'paragraph' }], type: 'doc', version: 1 }), notANode)
-  assert.equal(fault({ content: [{ marks: [{ attrs, type: 'link' }], text: 'x', type: 'text' }], type: 'doc', version: 1 }), notANode)
+  assert.equal(fault({ content: [{ attrs, type: 'paragraph' }], type: 'doc', version: 1 }), holdsItself)
+  assert.equal(fault({ content: [{ marks: [{ attrs, type: 'link' }], text: 'x', type: 'text' }], type: 'doc', version: 1 }), holdsItself)
   assert.equal(isAdfDocument({ content: [{ attrs, type: 'paragraph' }], type: 'doc', version: 1 }), false)
   const bold = { type: 'strong' }
   const text = { marks: [bold], text: 'x', type: 'text' }