chore: add regression tests for old lockfile warning

Ref: npm/cli#3721

Prior to [this change](c7f2370#diff-a22bf0383032b8f318ebe49a4e41b34bcc98e2c10d18322f619edcd041a27483R333-R334)
reifying with no package-lock or a package-lock with a merge conflict
would result in an old lockfile warning. This adds regression tests to
explicitly test both those scenarios.

test/arborist/build-ideal-tree.js

@@ -978,6 +978,52 @@ t.test('complete build for project with old lockfile', async t => {
   ])
 })
 
+t.test('no old lockfile warning with no package-lock', async t => {
+  const fixt = t.testdir({
+    node_modules: {
+      abbrev: {
+        'package.json': JSON.stringify({
+          name: 'abbrev',
+          version: '1.1.1',
+        }),
+      },
+    },
+    'package.json': JSON.stringify({
+      name: 'no-package-lock',
+      dependencies: {
+        abbrev: '1',
+      },
+    }),
+  })
+  const checkLogs = warningTracker()
+  await newArb(fixt).reify()
+  t.strictSame(checkLogs(), [])
+})
+
+t.test('no old lockfile warning with a conflict package-lock', async t => {
+  const fixt = t.testdir({
+    node_modules: {
+      abbrev: {
+        'package.json': JSON.stringify({
+          name: 'abbrev',
+          version: '1.1.1',
+        }),
+      },
+    },
+    'package.json': JSON.stringify({
+      name: 'conflict-package-lock',
+      dependencies: {
+        abbrev: '1',
+      },
+    }),
+    'package-lock.json': fs.readFileSync(resolve(fixtures, 'conflict-package-lock', 'package-lock.json'))
+  })
+
+  const checkLogs = warningTracker()
+  await newArb(fixt).reify()
+  t.strictSame(checkLogs(), [])
+})
+
 t.test('override a conflict with the root dep (with force)', async t => {
   const path = resolve(fixtures, 'testing-peer-dep-conflict-chain/override')
   // note: fails because this is the root dep, unless --force used