diff --git a/tests/cst.ts b/tests/cst.ts
new file mode 100644
index 00000000..7100e8f6
--- /dev/null
+++ b/tests/cst.ts
@@ -0,0 +1,197 @@
+import { CST, Parser } from 'yaml'
+import { source } from './_utils'
+
+function cstDoc(src: string) {
+  const tokens = Array.from(new Parser().parse(src))
+  expect(tokens).toHaveLength(1)
+  expect(tokens[0].type).toBe('document')
+  return tokens[0] as CST.Document
+}
+
+describe('CST.visit', () => {
+  test('Visit paths in order', () => {
+    const doc = cstDoc(source`
+      foo:
+        - baz
+        - [ bar: 42 ]
+      ? { fuzz, ball }
+      : fii
+    `)
+    const paths: CST.VisitPath[] = []
+    CST.visit(doc, (_item, path) => {
+      paths.push(path)
+    })
+    expect(paths).toMatchObject([
+      [],
+      [['value', 0]],
+      [
+        ['value', 0],
+        ['value', 0]
+      ],
+      [
+        ['value', 0],
+        ['value', 1]
+      ],
+      [
+        ['value', 0],
+        ['value', 1],
+        ['value', 0]
+      ],
+      [['value', 1]],
+      [
+        ['value', 1],
+        ['key', 0]
+      ],
+      [
+        ['value', 1],
+        ['key', 1]
+      ]
+    ])
+  })
+
+  test('break visit', () => {
+    const doc = cstDoc(source`
+      - " foo"
+      - "foo"
+      - "bar"
+    `)
+    let visits = 0
+    CST.visit(doc, item => {
+      visits += 1
+      const scalar = CST.resolveAsScalar(item.value)
+      if (scalar?.value === 'foo') return CST.visit.BREAK
+    })
+    expect(visits).toBe(3)
+  })
+
+  test('remove item', () => {
+    const doc = cstDoc(source`
+      -  " foo"
+      - "foo"
+      - "bar"
+    `)
+    let visits = 0
+    CST.visit(doc, item => {
+      visits += 1
+      const scalar = CST.resolveAsScalar(item.value)
+      if (scalar?.value === 'foo') return CST.visit.REMOVE
+    })
+    expect(visits).toBe(4)
+    expect(CST.stringify(doc)).toBe(source`
+      -  " foo"
+      - "bar"
+    `)
+  })
+
+  test('replace value with block scalar in seq', () => {
+    const doc = cstDoc(source`
+      -  " foo"
+      - "foo"
+      - "bar"
+    `)
+    let visits = 0
+    CST.visit(doc, item => {
+      visits += 1
+      if (item.value) {
+        const scalar = CST.resolveAsScalar(item.value)
+        if (scalar?.value === 'foo')
+          CST.setScalarValue(item.value, 'foo', { type: 'BLOCK_LITERAL' })
+      }
+    })
+    expect(visits).toBe(4)
+    expect(CST.stringify(doc)).toBe(source`
+      -  " foo"
+      - |-
+        foo
+      - "bar"
+    `)
+  })
+
+  test('add item', () => {
+    const doc = cstDoc(source`
+      -  " foo"
+      - "foo"
+      - "bar"
+    `)
+    let visits = 0
+    CST.visit(doc, (item, path) => {
+      visits += 1
+      if (CST.isScalar(item.value)) {
+        const scalar = CST.resolveAsScalar(item.value)
+        if (scalar?.value === 'foo') {
+          const parent = CST.visit.parentCollection(doc, path)
+          const idx = path[path.length - 1][1]
+          const { indent } = item.value
+          parent.items.splice(idx, 0, {
+            start: item.start.slice(),
+            value: CST.createScalarToken('hip', { indent })
+          })
+          return idx + 2
+        }
+      }
+    })
+    expect(visits).toBe(4)
+    expect(CST.stringify(doc)).toBe(source`
+      -  " foo"
+      - hip
+      - "foo"
+      - "bar"
+    `)
+  })
+
+  test('replace value with flow scalar in map', () => {
+    const doc = cstDoc(source`
+      - a:  A
+        b: B\t#comment
+        c: C
+    `)
+    let visits = 0
+    CST.visit(doc, item => {
+      visits += 1
+      if (item.value) {
+        const scalar = CST.resolveAsScalar(item.value)
+        if (scalar?.value === 'B') {
+          CST.setScalarValue(item.value, 'foo\n\nbar', { afterKey: !!item.key })
+        }
+      }
+    })
+    expect(visits).toBe(5)
+    expect(CST.stringify(doc)).toBe(source`
+      - a:  A
+        b: foo
+
+
+          bar\t#comment
+        c: C
+    `)
+  })
+
+  test('skip children', () => {
+    const doc = cstDoc(source`
+      - " foo"
+      - [ foo, 13, 42 ]
+      - "bar"
+    `)
+    let visits = 0
+    CST.visit(doc, item => {
+      visits += 1
+      if (item.value?.type === 'flow-collection') return CST.visit.SKIP
+    })
+    expect(visits).toBe(4)
+  })
+
+  test('set next index', () => {
+    const doc = cstDoc(source`
+      - "foo"
+      - [ foo, 13, 42 ]
+      - "bar"
+    `)
+    let visits = 0
+    CST.visit(doc, item => {
+      visits += 1
+      const scalar = CST.resolveAsScalar(item.value)
+      if (scalar?.value === 'foo') return 2
+    })
+    expect(visits).toBe(3)
+  })
+})