feat: add npm diffruyadorno/npm-diff

- As proposed in RFC: https://github.com/npm/rfcs/pull/144

PR-URL: https://github.com/npm/cli/pull/1319
Credit: @ruyadorno
Close: #1319
Reviewed-by: @isaacs

1 files changed, 1159 insertions, 0 deletions

diff --git a/test/lib/diff.js b/test/lib/diff.js
new file mode 100644
index 000000000..926c54fdf
--- /dev/null
+++ b/test/lib/diff.js
@@ -0,0 +1,1159 @@
+const { resolve } = require('path')
+const t = require('tap')
+const requireInject = require('require-inject')
+
+const noop = () => null
+let libnpmdiff = noop
+let rlp = () => 'foo'
+const defaultFlatOptions = {
+  defaultTag: 'latest',
+  diff: [],
+  diffUnified: null,
+  diffIgnoreAllSpace: false,
+  diffNoPrefix: false,
+  diffSrcPrefix: '',
+  diffDstPrefix: '',
+  diffText: false,
+  prefix: '.',
+  savePrefix: '^',
+}
+const npm = {
+  globalDir: __dirname,
+  flatOptions: { ...defaultFlatOptions },
+  get prefix () {
+    return this.flatOptions.prefix
+  },
+}
+const mocks = {
+  npmlog: { info: noop, verbose: noop },
+  libnpmdiff: (...args) => libnpmdiff(...args),
+  'npm-registry-fetch': async () => ({}),
+  '../../lib/npm.js': npm,
+  '../../lib/utils/output.js': noop,
+  '../../lib/utils/read-local-package.js': async () => rlp(),
+  '../../lib/utils/usage.js': () => 'usage instructions',
+}
+
+t.afterEach(cb => {
+  npm.flatOptions = { ...defaultFlatOptions }
+  libnpmdiff = noop
+  rlp = () => 'foo'
+  npm.globalDir = __dirname
+  cb()
+})
+
+const diff = requireInject('../../lib/diff.js', mocks)
+
+t.test('no args', t => {
+  t.test('in a project dir', t => {
+    t.plan(3)
+
+    const path = t.testdir({})
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'foo@latest', 'should have default spec comparison')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('no args, missing package.json name in cwd', t => {
+    rlp = () => undefined
+
+    diff([], err => {
+      t.match(
+        err,
+        /Needs multiple arguments to compare or run from a project dir./,
+        'should throw EDIFF error msg'
+      )
+      t.end()
+    })
+  })
+
+  t.test('no args, missing package.json in cwd', t => {
+    rlp = () => {
+      throw new Error('ERR')
+    }
+
+    diff([], err => {
+      t.match(
+        err,
+        /Needs multiple arguments to compare or run from a project dir./,
+        'should throw EDIFF error msg'
+      )
+      t.end()
+    })
+  })
+
+  t.end()
+})
+
+t.test('single arg', t => {
+  t.test('spec using cwd package name', t => {
+    t.plan(3)
+
+    const path = t.testdir({})
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'foo@1.0.0', 'should forward single spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.diff = ['foo@1.0.0']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('unknown spec, no package.json', t => {
+    const path = t.testdir({})
+    rlp = () => {
+      throw new Error('ERR')
+    }
+
+    npm.flatOptions.diff = ['foo@1.0.0']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      t.match(
+        err,
+        /Needs multiple arguments to compare or run from a project dir./,
+        'should throw usage error'
+      )
+      t.end()
+    })
+  })
+
+  t.test('spec using semver range', t => {
+    t.plan(3)
+
+    const path = t.testdir({})
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'foo@~1.0.0', 'should forward single spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.diff = ['foo@~1.0.0']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('version', t => {
+    t.plan(3)
+
+    const path = t.testdir({})
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'foo@2.1.4', 'should convert to expected first spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.diff = ['2.1.4']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('version, no package.json', t => {
+    rlp = () => {
+      throw new Error('ERR')
+    }
+
+    npm.flatOptions.diff = ['2.1.4']
+    diff([], err => {
+      t.match(
+        err,
+        /Needs multiple arguments to compare or run from a project dir./,
+        'should throw an error message explaining usage'
+      )
+      t.end()
+    })
+  })
+
+  t.test('version, filtering by files', t => {
+    t.plan(3)
+
+    const path = t.testdir({})
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'foo@2.1.4', 'should use expected spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, {
+        ...npm.flatOptions,
+        diffFiles: [
+          './foo.js',
+          './bar.js',
+        ],
+      }, 'should forward flatOptions and diffFiles')
+    }
+
+    npm.flatOptions.diff = ['2.1.4']
+    npm.flatOptions.prefix = path
+    diff(['./foo.js', './bar.js'], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('spec is not a dep', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {},
+      'package.json': JSON.stringify({
+        name: 'my-project',
+      }),
+    })
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should have current spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+    }
+
+    npm.flatOptions.diff = ['bar@1.0.0']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('unknown package name', t => {
+    t.plan(3)
+
+    const path = t.testdir({
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'simple-output@latest', 'should forward single spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.diff = ['simple-output']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('unknown package name, no package.json', t => {
+    const path = t.testdir({})
+    rlp = () => {
+      throw new Error('ERR')
+    }
+
+    npm.flatOptions.diff = ['bar']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      t.match(
+        err,
+        /Needs multiple arguments to compare or run from a project dir./,
+        'should throw usage error'
+      )
+      t.end()
+    })
+  })
+
+  t.test('transform single direct dep name into spec comparison', t => {
+    t.plan(4)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    npm.flatOptions.diff = ['bar']
+    npm.flatOptions.prefix = path
+
+    const diff = requireInject('../../lib/diff.js', {
+      ...mocks,
+      pacote: {
+        packument: (spec) => {
+          t.equal(spec.name, 'bar', 'should have expected spec name')
+        },
+      },
+      'npm-pick-manifest': (packument, target) => {
+        t.equal(target, '^1.0.0', 'should use expected target')
+        return { version: '1.8.10' }
+      },
+      libnpmdiff: async ([a, b], opts) => {
+        t.equal(a, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+        t.equal(b, 'bar@1.8.10', 'should have possible semver range spec')
+      },
+    })
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('global space, transform single direct dep name', t => {
+    t.plan(4)
+
+    const path = t.testdir({
+      globalDir: {
+        lib: {
+          node_modules: {
+            lorem: {
+              'package.json': JSON.stringify({
+                name: 'lorem',
+                version: '2.0.0',
+              }),
+            },
+          },
+        },
+      },
+      project: {
+        node_modules: {
+          bar: {
+            'package.json': JSON.stringify({
+              name: 'bar',
+              version: '1.0.0',
+            }),
+          },
+        },
+        'package.json': JSON.stringify({
+          name: 'my-project',
+          dependencies: {
+            bar: '^1.0.0',
+          },
+        }),
+      },
+    })
+
+    npm.flatOptions.global = true
+    npm.flatOptions.diff = ['lorem']
+    npm.flatOptions.prefix = resolve(path, 'project')
+    npm.globalDir = resolve(path, 'globalDir/lib/node_modules')
+
+    const diff = requireInject('../../lib/diff.js', {
+      ...mocks,
+      pacote: {
+        packument: (spec) => {
+          t.equal(spec.name, 'lorem', 'should have expected spec name')
+        },
+      },
+      'npm-pick-manifest': (packument, target) => {
+        t.equal(target, '*', 'should always want latest in global space')
+        return { version: '2.1.0' }
+      },
+      libnpmdiff: async ([a, b], opts) => {
+        t.equal(a, `lorem@file:${resolve(path, 'globalDir/lib/node_modules/lorem')}`, 'should target local node_modules pkg')
+        t.equal(b, 'lorem@2.1.0', 'should have possible semver range spec')
+      },
+    })
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('transform single spec into spec comparison', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+      t.equal(b, 'bar@2.0.0', 'should have expected comparison spec')
+    }
+
+    npm.flatOptions.diff = ['bar@2.0.0']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('transform single spec from transitive deps', t => {
+    t.plan(4)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+            dependencies: {
+              lorem: '^2.0.0',
+            },
+          }),
+        },
+        lorem: {
+          'package.json': JSON.stringify({
+            name: 'lorem',
+            version: '2.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    const diff = requireInject('../../lib/diff.js', {
+      ...mocks,
+      '../../lib/utils/read-local-package.js': async () => 'my-project',
+      pacote: {
+        packument: (spec) => {
+          t.equal(spec.name, 'lorem', 'should have expected spec name')
+        },
+      },
+      'npm-pick-manifest': (packument, target) => {
+        t.equal(target, '^2.0.0', 'should target first semver-range spec found')
+        return { version: '2.2.2' }
+      },
+      libnpmdiff: async ([a, b], opts) => {
+        t.equal(a, `lorem@file:${resolve(path, 'node_modules/lorem')}`, 'should target local node_modules pkg')
+        t.equal(b, 'lorem@2.2.2', 'should have expected target spec')
+      },
+    })
+
+    npm.flatOptions.diff = ['lorem']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('missing actual tree', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      'package.json': JSON.stringify({
+        name: 'my-project',
+      }),
+    })
+
+    const diff = requireInject('../../lib/diff.js', {
+      ...mocks,
+      '../../lib/utils/read-local-package.js': async () => 'my-project',
+      '@npmcli/arborist': class {
+        constructor () {
+          throw new Error('ERR')
+        }
+      },
+      libnpmdiff: async ([a, b], opts) => {
+        t.equal(a, 'lorem@latest', 'should target latest version of pkg name')
+        t.equal(b, `file:${path}`, 'should target current cwd')
+      },
+    })
+
+    npm.flatOptions.diff = ['lorem']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('unknown package name', t => {
+    t.plan(2)
+
+    const path = t.testdir({})
+    rlp = async () => undefined
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@latest', 'should target latest tag of name')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+    }
+
+    npm.flatOptions.diff = ['bar']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('use project name in project dir', t => {
+    t.plan(2)
+
+    const path = t.testdir({})
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'my-project@latest', 'should target latest tag of name')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+    }
+
+    npm.flatOptions.diff = ['my-project']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('dir spec type', t => {
+    t.plan(2)
+
+    const path = t.testdir({})
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'file:/path/to/other-dir', 'should target dir')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+    }
+
+    npm.flatOptions.diff = ['/path/to/other-dir']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('unsupported spec type', t => {
+    rlp = async () => 'my-project'
+
+    npm.flatOptions.diff = ['git+https://github.com/user/foo']
+
+    diff([], err => {
+      t.match(
+        err,
+        /Spec type not supported./,
+        'should throw spec type not supported error.'
+      )
+      t.end()
+    })
+  })
+
+  t.end()
+})
+
+t.test('first arg is a qualified spec', t => {
+  t.test('second arg is ALSO a qualified spec', t => {
+    t.plan(3)
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should set expected first spec')
+      t.equal(b, 'bar@^2.0.0', 'should set expected second spec')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.diff = ['bar@1.0.0', 'bar@^2.0.0']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a known dependency name', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@2.0.0', 'should set expected first spec')
+      t.equal(b, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['bar@2.0.0', 'bar']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a valid semver version', t => {
+    t.plan(2)
+
+    npm.flatOptions.diff = ['bar@1.0.0', '2.0.0']
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should set expected first spec')
+      t.equal(b, 'bar@2.0.0', 'should use name from first arg')
+    }
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is an unknown dependency name', t => {
+    t.plan(2)
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should set expected first spec')
+      t.equal(b, 'bar-fork@latest', 'should target latest tag if not a dep')
+    }
+
+    npm.flatOptions.diff = ['bar@1.0.0', 'bar-fork']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.end()
+})
+
+t.test('first arg is a known dependency name', t => {
+  t.test('second arg is a qualified spec', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+      t.equal(b, 'bar@2.0.0', 'should set expected second spec')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['bar', 'bar@2.0.0']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is ALSO a known dependency', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+        'bar-fork': {
+          'package.json': JSON.stringify({
+            name: 'bar-fork',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+      t.equal(b, `bar-fork@file:${resolve(path, 'node_modules/bar-fork')}`, 'should target fork local node_modules pkg')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['bar', 'bar-fork']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a valid semver version', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+      t.equal(b, 'bar@2.0.0', 'should use package name from first arg')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['bar', '2.0.0']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is an unknown dependency name', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '1.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+      t.equal(b, 'bar-fork@latest', 'should set expected second spec')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['bar', 'bar-fork']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.end()
+})
+
+t.test('first arg is a valid semver range', t => {
+  t.test('second arg is a qualified spec', t => {
+    t.plan(2)
+
+    npm.flatOptions.diff = ['1.0.0', 'bar@2.0.0']
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should use name from second arg')
+      t.equal(b, 'bar@2.0.0', 'should use expected spec')
+    }
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a known dependency', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '2.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should use name from second arg')
+      t.equal(b, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should set expected second spec from nm')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['1.0.0', 'bar']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is ALSO a semver version', t => {
+    t.plan(2)
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'my-project@1.0.0', 'should use name from project dir')
+      t.equal(b, 'my-project@2.0.0', 'should use name from project dir')
+    }
+
+    npm.flatOptions.diff = ['1.0.0', '2.0.0']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is ALSO a semver version BUT cwd not a project dir', t => {
+    const path = t.testdir({})
+    rlp = () => {
+      throw new Error('ERR')
+    }
+
+    npm.flatOptions.diff = ['1.0.0', '2.0.0']
+    npm.flatOptions.prefix = path
+    diff([], err => {
+      t.match(
+        err,
+        /Needs to be run from a project dir in order to diff two versions./,
+        'should throw two versions need project dir error usage msg'
+      )
+      t.end()
+    })
+  })
+
+  t.test('second arg is an unknown dependency name', t => {
+    t.plan(2)
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@1.0.0', 'should use name from second arg')
+      t.equal(b, 'bar@latest', 'should compare against latest tag')
+    }
+
+    npm.flatOptions.diff = ['1.0.0', 'bar']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a qualified spec, missing actual tree', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      'package.json': JSON.stringify({
+        name: 'my-project',
+      }),
+    })
+
+    const diff = requireInject('../../lib/diff.js', {
+      ...mocks,
+      '../../lib/utils/read-local-package.js': async () => 'my-project',
+      '@npmcli/arborist': class {
+        constructor () {
+          throw new Error('ERR')
+        }
+      },
+      libnpmdiff: async ([a, b], opts) => {
+        t.equal(a, 'lorem@1.0.0', 'should target latest version of pkg name')
+        t.equal(b, 'lorem@2.0.0', 'should target expected spec')
+      },
+    })
+
+    npm.flatOptions.diff = ['1.0.0', 'lorem@2.0.0']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.end()
+})
+
+t.test('first arg is an unknown dependency name', t => {
+  t.test('second arg is a qualified spec', t => {
+    t.plan(3)
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@latest', 'should set expected first spec')
+      t.equal(b, 'bar@2.0.0', 'should set expected second spec')
+      t.match(opts, npm.flatOptions, 'should forward flat options')
+    }
+
+    npm.flatOptions.diff = ['bar', 'bar@2.0.0']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a known dependency', t => {
+    t.plan(2)
+
+    const path = t.testdir({
+      node_modules: {
+        bar: {
+          'package.json': JSON.stringify({
+            name: 'bar',
+            version: '2.0.0',
+          }),
+        },
+      },
+      'package.json': JSON.stringify({
+        name: 'my-project',
+        dependencies: {
+          bar: '^1.0.0',
+        },
+      }),
+    })
+
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar-fork@latest', 'should use latest tag')
+      t.equal(b, `bar@file:${resolve(path, 'node_modules/bar')}`, 'should target local node_modules pkg')
+    }
+
+    npm.flatOptions.prefix = path
+    npm.flatOptions.diff = ['bar-fork', 'bar']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is a valid semver version', t => {
+    t.plan(2)
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@latest', 'should use latest tag')
+      t.equal(b, 'bar@^1.0.0', 'should use name from first arg')
+    }
+
+    npm.flatOptions.diff = ['bar', '^1.0.0']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('second arg is ALSO an unknown dependency name', t => {
+    t.plan(2)
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@latest', 'should use latest tag')
+      t.equal(b, 'bar-fork@latest', 'should use latest tag')
+    }
+
+    npm.flatOptions.diff = ['bar', 'bar-fork']
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('cwd not a project dir', t => {
+    t.plan(2)
+
+    const path = t.testdir({})
+    rlp = () => {
+      throw new Error('ERR')
+    }
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'bar@latest', 'should use latest tag')
+      t.equal(b, 'bar-fork@latest', 'should use latest tag')
+    }
+
+    npm.flatOptions.diff = ['bar', 'bar-fork']
+    npm.flatOptions.prefix = path
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.end()
+})
+
+t.test('various options', t => {
+  t.test('using --name-only option', t => {
+    t.plan(1)
+
+    npm.flatOptions.diffNameOnly = true
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.match(opts, {
+        ...npm.flatOptions,
+        diffNameOnly: true,
+      }, 'should forward nameOnly=true option')
+    }
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('set files after both versions', t => {
+    t.plan(3)
+
+    npm.flatOptions.diff = ['2.1.4', '3.0.0']
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'foo@2.1.4', 'should use expected spec')
+      t.equal(b, 'foo@3.0.0', 'should use expected spec')
+      t.match(opts, {
+        ...npm.flatOptions,
+        diffFiles: [
+          './foo.js',
+          './bar.js',
+        ],
+      }, 'should forward diffFiles values')
+    }
+
+    diff(['./foo.js', './bar.js'], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('set files no diff args', t => {
+    t.plan(3)
+
+    const path = t.testdir({})
+    rlp = async () => 'my-project'
+    libnpmdiff = async ([a, b], opts) => {
+      t.equal(a, 'my-project@latest', 'should have default spec')
+      t.equal(b, `file:${path}`, 'should compare to cwd')
+      t.match(opts, {
+        ...npm.flatOptions,
+        diffFiles: [
+          './foo.js',
+          './bar.js',
+        ],
+      }, 'should forward all remaining items as filenames')
+    }
+
+    npm.flatOptions.prefix = path
+    diff(['./foo.js', './bar.js'], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.test('using diff option', t => {
+    t.plan(1)
+
+    npm.flatOptions.diffContext = 5
+    npm.flatOptions.diffIgnoreWhitespace = true
+    npm.flatOptions.diffNoPrefix = false
+    npm.flatOptions.diffSrcPrefix = 'foo/'
+    npm.flatOptions.diffDstPrefix = 'bar/'
+    npm.flatOptions.diffText = true
+
+    libnpmdiff = async ([a, b], opts) => {
+      t.match(opts, {
+        ...npm.flatOptions,
+        diffContext: 5,
+        diffIgnoreWhitespace: true,
+        diffNoPrefix: false,
+        diffSrcPrefix: 'foo/',
+        diffDstPrefix: 'bar/',
+        diffText: true,
+      }, 'should forward diff options')
+    }
+
+    diff([], err => {
+      if (err)
+        throw err
+    })
+  })
+
+  t.end()
+})
+
+t.test('too many args', t => {
+  npm.flatOptions.diff = ['a', 'b', 'c']
+  diff([], err => {
+    t.match(
+      err,
+      /Can't use more than two --diff arguments./,
+      'should throw usage error'
+    )
+    t.end()
+  })
+})