[#493] cmd/node: Add .env file for tests

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

cmd/neofs-node/config/test/config.go

@@ -1,15 +1,30 @@
 package configtest
 
-import "github.com/nspcc-dev/neofs-node/cmd/neofs-node/config"
+import (
+	"bufio"
+	"os"
+	"strings"
+
+	"github.com/nspcc-dev/neofs-node/cmd/neofs-node/config"
+)
 
 func fromFile(path string) *config.Config {
 	var p config.Prm
 
+	os.Clearenv() // ENVs have priority over config files so we do this in tests
+
 	return config.New(p,
 		config.WithConfigFile(path),
 	)
 }
 
+func fromEnvFile(path string) *config.Config {
+	var p config.Prm
+
+	loadEnv(path) // github.com/joho/godotenv can do that as well
+	return config.New(p)
+}
+
 func forEachFile(paths []string, f func(*config.Config)) {
 	for i := range paths {
 		f(fromFile(paths[i]))
@@ -26,9 +41,37 @@ func ForEachFileType(pref string, f func(*config.Config)) {
 	}, f)
 }
 
+// ForEnvFileType creates config from `<pref>.env` file.
+func ForEnvFileType(pref string, f func(*config.Config)) {
+	f(fromEnvFile(pref + ".env"))
+}
+
 // EmptyConfig returns config without any values and sections.
 func EmptyConfig() *config.Config {
 	var p config.Prm
 
 	return config.New(p)
 }
+
+// loadEnv reads .env file, parses `X=Y` records and sets OS ENVs.
+func loadEnv(path string) {
+	f, err := os.Open(path)
+	if err != nil {
+		panic("can't open .env file")
+	}
+
+	defer f.Close()
+
+	scanner := bufio.NewScanner(f)
+	for scanner.Scan() {
+		pair := strings.Split(scanner.Text(), "=")
+		if len(pair) != 2 {
+			continue
+		}
+
+		err = os.Setenv(pair[0], pair[1])
+		if err != nil {
+			panic("can't set environment variable")
+		}
+	}
+}