Fail if error is thrown while awaiting a Promise

This was causing a test in make-fetch-happen to hang silently and time
out rather than failing appropriately.

Note that this can only happen if the error is thrown _outside_ of the
Promise flow of control.  Throws from withing .then()/.catch() methods
will reject the promise, which may be what you want.  If an EventEmitter
or something throws an error, tap will still track it, but the Promise
chain might not.  If it makes it to tap, then the Promise chain is
probably broken.

lib/test.js

@@ -864,6 +864,11 @@ class Test extends Base {
       if (!proxy)
         this.end(IMPLICIT)
     }
+    // threw while waiting for a promise to resolve.
+    // probably it's not ever gonna.
+    if (this.occupied && this.occupied instanceof Waiter)
+      this.occupied.abort(new Error('error thrown while awaiting Promise'))
+
     this.process()
   }
 

tap-snapshots/test-test.js-TAP.test.js

@@ -3187,3 +3187,51 @@ not ok 1 - child test # {time}
 # failed 1 test
 
 `
+
+exports[`test/test.js TAP throw while waiting on a resolving promise > result 1`] = `
+TAP version 13
+# Subtest
+    not ok 1 - expect resolving Promise
+      ---
+      at:
+        line: #
+        column: #
+        file: test/test.js
+      found:
+        !error
+        name: Error
+        message: error thrown while awaiting Promise
+        stack: |
+          {STACK}
+      source: |2
+            setTimeout(() => t.threw(new Error('poop')))
+            return t.resolveMatch(() => new Promise(() => {}), 'never resolves')
+        --^
+          })
+          tt.end()
+      ...
+    
+    not ok 2 - poop
+      ---
+      at:
+        line: #
+        column: #
+        file: test/test.js
+      source: |2
+          tt.test(t => {
+            setTimeout(() => t.threw(new Error('poop')))
+        --^
+            return t.resolveMatch(() => new Promise(() => {}), 'never resolves')
+          })
+      stack: |
+        {STACK}
+      ...
+    
+    1..2
+    # failed 2 of 2 tests
+not ok 1 # {time}
+
+1..1
+# failed 1 test
+
+`

test/test.js

@@ -1153,3 +1153,20 @@ t.test('endAll with sub while waiting on a resolving promise', t => {
   tt.test(t => t.resolveMatch(() => new Promise(() => {}), 'never resolves'))
   setTimeout(() => tt.endAll())
 })
+
+t.test('throw while waiting on a resolving promise', t => {
+  t.plan(1)
+  const tt = new Test()
+  tt.setEncoding('utf8')
+  const buf = []
+  tt.on('data', c => buf.push(c))
+  tt.on('end', () => {
+    const result = buf.join('')
+    t.matchSnapshot(result, 'result')
+  })
+  tt.test(t => {
+    setTimeout(() => t.threw(new Error('poop')))
+    return t.resolveMatch(() => new Promise(() => {}), 'never resolves')
+  })
+  tt.end()
+})