testing: provide additional information when test funcs panic

Flush the output log up to the root when a test panics. Prior to
this change, only the current test's output log was flushed to its
parent, resulting in no output when a subtest panics.

For the following test function:

	func Test(t *testing.T) {
		for i, test := range []int{1, 0, 2} {
			t.Run(fmt.Sprintf("%v/%v", i, test), func(t *testing.T) {
				_ = 1 / test
			})
		}
	}

Output before this change:

	panic: runtime error: integer divide by zero [recovered]
		panic: runtime error: integer divide by zero
	(stack trace follows)

Output after this change:

	--- FAIL: Test (0.00s)
	    --- FAIL: Test/1/0 (0.00s)
	panic: runtime error: integer divide by zero [recovered]
	(stack trace follows)

Fixes #32121

Change-Id: Ifee07ccc005f0493a902190a8be734943123b6b7
Reviewed-on: https://go-review.googlesource.com/c/go/+/179599
Run-TryBot: Damien Neil <dneil@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

2 files changed, 36 insertions, 0 deletions

diff --git a/src/cmd/internal/test2json/testdata/panic.json b/src/cmd/internal/test2json/testdata/panic.json
new file mode 100644
index 0000000000..f99679c2e2
--- /dev/null
+++ b/src/cmd/internal/test2json/testdata/panic.json
@@ -0,0 +1,19 @@
+{"Action":"output","Test":"TestPanic","Output":"--- FAIL: TestPanic (0.00s)\n"}
+{"Action":"output","Test":"TestPanic","Output":"panic: oops [recovered]\n"}
+{"Action":"output","Test":"TestPanic","Output":"\tpanic: oops\n"}
+{"Action":"output","Test":"TestPanic","Output":"\n"}
+{"Action":"output","Test":"TestPanic","Output":"goroutine 7 [running]:\n"}
+{"Action":"output","Test":"TestPanic","Output":"testing.tRunner.func1(0xc000092100)\n"}
+{"Action":"output","Test":"TestPanic","Output":"\t/go/src/testing/testing.go:874 +0x3a3\n"}
+{"Action":"output","Test":"TestPanic","Output":"panic(0x1110ea0, 0x116aea0)\n"}
+{"Action":"output","Test":"TestPanic","Output":"\t/go/src/runtime/panic.go:679 +0x1b2\n"}
+{"Action":"output","Test":"TestPanic","Output":"command-line-arguments.TestPanic(0xc000092100)\n"}
+{"Action":"output","Test":"TestPanic","Output":"\ta_test.go:6 +0x39\n"}
+{"Action":"output","Test":"TestPanic","Output":"testing.tRunner(0xc000092100, 0x114f500)\n"}
+{"Action":"output","Test":"TestPanic","Output":"\tgo/src/testing/testing.go:909 +0xc9\n"}
+{"Action":"output","Test":"TestPanic","Output":"created by testing.(*T).Run\n"}
+{"Action":"output","Test":"TestPanic","Output":"\tgo/src/testing/testing.go:960 +0x350\n"}
+{"Action":"output","Test":"TestPanic","Output":"FAIL\tcommand-line-arguments\t0.042s\n"}
+{"Action":"fail","Test":"TestPanic"}
+{"Action":"output","Output":"FAIL\n"}
+{"Action":"fail"}
diff --git a/src/cmd/internal/test2json/testdata/panic.test b/src/cmd/internal/test2json/testdata/panic.test
new file mode 100644
index 0000000000..517ebafeb5
--- /dev/null
+++ b/src/cmd/internal/test2json/testdata/panic.test
@@ -0,0 +1,17 @@
+--- FAIL: TestPanic (0.00s)
+panic: oops [recovered]
+	panic: oops
+
+goroutine 7 [running]:
+testing.tRunner.func1(0xc000092100)
+	/go/src/testing/testing.go:874 +0x3a3
+panic(0x1110ea0, 0x116aea0)
+	/go/src/runtime/panic.go:679 +0x1b2
+command-line-arguments.TestPanic(0xc000092100)
+	a_test.go:6 +0x39
+testing.tRunner(0xc000092100, 0x114f500)
+	go/src/testing/testing.go:909 +0xc9
+created by testing.(*T).Run
+	go/src/testing/testing.go:960 +0x350
+FAIL	command-line-arguments	0.042s
+FAIL