Improve test coverage reporting / accuracy (#7819)

* improve test coverage reporting / accuracy

* handle absolute coverpaths

* move tests into multiple files

* rename codecov.yml (https://github.com/codecov/support/issues/426)

cmd/platform/platform_test.go

@@ -0,0 +1,53 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+var coverprofileCounters map[string]int = make(map[string]int)
+
+func execArgs(t *testing.T, args []string) []string {
+	ret := []string{"-test.run", "ExecCommand"}
+	if coverprofile := flag.Lookup("test.coverprofile").Value.String(); coverprofile != "" {
+		dir := filepath.Dir(coverprofile)
+		base := filepath.Base(coverprofile)
+		baseParts := strings.SplitN(base, ".", 2)
+		coverprofileCounters[t.Name()] = coverprofileCounters[t.Name()] + 1
+		baseParts[0] = fmt.Sprintf("%v-%v-%v", baseParts[0], t.Name(), coverprofileCounters[t.Name()])
+		ret = append(ret, "-test.coverprofile", filepath.Join(dir, strings.Join(baseParts, ".")))
+	}
+	return append(append(ret, "--"), args...)
+}
+
+func checkCommand(t *testing.T, args ...string) string {
+	path, err := os.Executable()
+	require.NoError(t, err)
+	output, err := exec.Command(path, execArgs(t, args)...).CombinedOutput()
+	require.NoError(t, err, string(output))
+	return string(output)
+}
+
+func runCommand(t *testing.T, args ...string) error {
+	path, err := os.Executable()
+	require.NoError(t, err)
+	return exec.Command(path, execArgs(t, args)...).Run()
+}
+
+func TestExecCommand(t *testing.T) {
+	if filter := flag.Lookup("test.run").Value.String(); filter != "ExecCommand" {
+		t.Skip("use -run ExecCommand to execute a command via the test executable")
+	}
+	rootCmd.SetArgs(flag.Args())
+	require.NoError(t, rootCmd.Execute())
+}