code review 55780043: testing: diagnose buggy tests that panic(nil)

src/pkg/testing/testing.go

 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 // Package testing provides support for automated testing of Go packages.
 // It is intended to be used in concert with the ``go test'' command, which automates
 // execution of any function of the form
 //     func TestXxx(*testing.T)
 // where Xxx can be any alphanumeric string (but the first letter must not be in
 // [a-z]) and serves to identify the test routine.
@@ skipping 358 matching lines @@
 type InternalTest struct {
         Name string
         F    func(*T)
 }
 
 func tRunner(t *T, test *InternalTest) {
         // When this goroutine is done, either because test.F(t)
         // returned normally or because a test failure triggered
         // a call to runtime.Goexit, record the duration and send
         // a signal saying that the test is done.
+        var finished bool
         defer func() {
                 t.duration = time.Now().Sub(t.start)
                 // If the test panicked, print any test output before dying.
-                if err := recover(); err != nil {
+                err := recover()
+                if !finished && err == nil {
+                        err = fmt.Errorf("test executed panic(nil)")
+                }
+                if err != nil {
                         t.Fail()
                         t.report()
                         panic(err)
                 }
                 t.signal <- t
         }()
 
         t.start = time.Now()
         test.F(t)
+        finished = true
 }
 
 // An internal function but exported because it is cross-package; part of the implementation
 // of the "go test" command.
 func Main(matchString func(pat, str string) (bool, error), tests []InternalTest, benchmarks []InternalBenchmark, examples []InternalExample) {
         flag.Parse()
         parseCpuList()
 
         before()
         startAlarm()
@@ skipping 213 matching lines @@
                 if err != nil || cpu <= 0 {
                         fmt.Fprintf(os.Stderr, "testing: invalid value %q for -test.cpu\n", val)
                         os.Exit(1)
                 }
                 cpuList = append(cpuList, cpu)
         }
         if cpuList == nil {
                 cpuList = append(cpuList, runtime.GOMAXPROCS(-1))
         }
 }