test: Add tools to generate test coverage information

This patch adds some tooling and scripts to generate test coverage
information.

Unfortunately, this involves some hacks as Go does not have support for
generating coverage-enabled binaries, or merging coverage reports; but
overall it's not very intrusive.

test/util/gocovcat.go

@@ -0,0 +1,91 @@
+//usr/bin/env go run "$0" "$@"; exit $?
+//
+// From: https://git.lukeshu.com/go/cmd/gocovcat/
+//
+// +build ignore
+
+// Copyright 2017 Luke Shumaker <lukeshu@parabola.nu>
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+//
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+// Command gocovcat combines multiple go cover runs, and prints the
+// result on stdout.
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"sort"
+	"strconv"
+	"strings"
+)
+
+func handleErr(err error) {
+	if err != nil {
+		fmt.Fprintf(os.Stderr, "%v\n", err)
+		os.Exit(1)
+	}
+}
+
+func main() {
+	modeBool := false
+	blocks := map[string]int{}
+	for _, filename := range os.Args[1:] {
+		file, err := os.Open(filename)
+		handleErr(err)
+		buf := bufio.NewScanner(file)
+		for buf.Scan() {
+			line := buf.Text()
+
+			if strings.HasPrefix(line, "mode: ") {
+				m := strings.TrimPrefix(line, "mode: ")
+				switch m {
+				case "set":
+					modeBool = true
+				case "count", "atomic":
+					// do nothing
+				default:
+					fmt.Fprintf(os.Stderr, "Unrecognized mode: %s\n", m)
+					os.Exit(1)
+				}
+			} else {
+				sp := strings.LastIndexByte(line, ' ')
+				block := line[:sp]
+				cntStr := line[sp+1:]
+				cnt, err := strconv.Atoi(cntStr)
+				handleErr(err)
+				blocks[block] += cnt
+			}
+		}
+		handleErr(buf.Err())
+	}
+	keys := make([]string, 0, len(blocks))
+	for key := range blocks {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	modeStr := "count"
+	if modeBool {
+		modeStr = "set"
+	}
+	fmt.Printf("mode: %s\n", modeStr)
+	for _, block := range keys {
+		cnt := blocks[block]
+		if modeBool && cnt > 1 {
+			cnt = 1
+		}
+		fmt.Printf("%s %d\n", block, cnt)
+	}
+}