add fail-test file instead of dep, closes #2638 (#2728)

original author of this file is @ebuchman:

https://github.com/ebuchman/fail-test

libs/fail/fail.go

@@ -0,0 +1,78 @@
+package fail
+
+import (
+	"fmt"
+	"math/rand"
+	"os"
+	"strconv"
+)
+
+var callIndexToFail int
+
+func init() {
+	callIndexToFailS := os.Getenv("FAIL_TEST_INDEX")
+
+	if callIndexToFailS == "" {
+		callIndexToFail = -1
+	} else {
+		var err error
+		callIndexToFail, err = strconv.Atoi(callIndexToFailS)
+		if err != nil {
+			callIndexToFail = -1
+		}
+	}
+}
+
+// Fail when FAIL_TEST_INDEX == callIndex
+var (
+	callIndex int //indexes Fail calls
+
+	callRandIndex       int  // indexes a run of FailRand calls
+	callRandIndexToFail = -1 // the callRandIndex to fail on in FailRand
+)
+
+func Fail() {
+	if callIndexToFail < 0 {
+		return
+	}
+
+	if callIndex == callIndexToFail {
+		Exit()
+	}
+
+	callIndex += 1
+}
+
+// FailRand should be called n successive times.
+// It will fail on a random one of those calls
+// n must be greater than 0
+func FailRand(n int) {
+	if callIndexToFail < 0 {
+		return
+	}
+
+	if callRandIndexToFail < 0 {
+		// first call in the loop, pick a random index to fail at
+		callRandIndexToFail = rand.Intn(n)
+		callRandIndex = 0
+	}
+
+	if callIndex == callIndexToFail {
+		if callRandIndex == callRandIndexToFail {
+			Exit()
+		}
+	}
+
+	callRandIndex += 1
+
+	if callRandIndex == n {
+		callIndex += 1
+	}
+}
+
+func Exit() {
+	fmt.Printf("*** fail-test %d ***\n", callIndex)
+	proc, _ := os.FindProcess(os.Getpid())
+	proc.Signal(os.Interrupt)
+	//	panic(fmt.Sprintf("*** fail-test %d ***", callIndex))
+}