Include diags for first missing test on plan failures

lib/test.js

@@ -1050,8 +1050,16 @@ Test.prototype._end = function (implicit) {
   // guard against that with the 'ending' flag
   this._ending = true
   var missing = this._plan - this._count
+  var addMissingTestDiag = true
   while (missing > 0) {
-    this.fail('missing test', { at: false })
+    this.fail('missing test', {
+      at: false,
+      plan: this._plan,
+      count: this._count,
+      missing: missing,
+      diagnostic: addMissingTestDiag
+    })
+    addMissingTestDiag = false
     missing--
   }
 

test/test/plan-too-many.tap

@@ -11,6 +11,9 @@ TAP version 13
           {"at":{"column":5,"file":"test/test/plan-too-many.js","line":7},"count":1,"plan":8,"source":"t.test('grandchild', function (tt) {\n"}
           ...
         not ok 3 - missing test
+          ---
+          {"count":2,"missing":6,"plan":8}
+          ...
         not ok 4 - missing test
         not ok 5 - missing test
         not ok 6 - missing test
@@ -23,6 +26,9 @@ TAP version 13
       ...
 
     not ok 4 - missing test
+      ---
+      {"count":3,"missing":6,"plan":9}
+      ...
     not ok 5 - missing test
     not ok 6 - missing test
     not ok 7 - missing test

test/test/throws-and-plans.tap

@@ -48,6 +48,9 @@ not ok 3 - no assert only throw ___/# time=[0-9.]+(ms)?/~~~
           {"at":{"column":11,"file":"test/test/throws-and-plans.js","line":39},"message":"Error: pwnSync","source":"throw new Error('pwnSync')\n","test":"sync thrower"}
           ...
         not ok 3 - missing test
+          ---
+          {"count":2,"missing":6,"plan":8}
+          ...
         not ok 4 - missing test
         not ok 5 - missing test
         not ok 6 - missing test
@@ -68,6 +71,9 @@ not ok 3 - no assert only throw ___/# time=[0-9.]+(ms)?/~~~
           {"at":{"column":13,"file":"test/test/throws-and-plans.js","line":18},"message":"Error: pwn","source":"throw new Error('pwn')\n","test":"async thrower"}
           ...
         not ok 4 - missing test
+          ---
+          {"count":3,"missing":5,"plan":8}
+          ...
         not ok 5 - missing test
         not ok 6 - missing test
         not ok 7 - missing test