all: Refactor to nonglobal Viper, i18n etc.

This is a final rewrite that removes all the global state in Hugo, which also enables
the use if `t.Parallel` in tests.

Updates #2701
Fixes #3016

helpers/testhelpers_test.go

@@ -0,0 +1,37 @@
+package helpers
+
+import (
+	"github.com/spf13/viper"
+
+	"github.com/spf13/hugo/hugofs"
+)
+
+func newTestPathSpec(fs *hugofs.Fs, v *viper.Viper) *PathSpec {
+	l := NewDefaultLanguage(v)
+	return NewPathSpec(fs, l)
+}
+
+func newTestDefaultPathSpec(configKeyValues ...interface{}) *PathSpec {
+	v := viper.New()
+	fs := hugofs.NewMem(v)
+	cfg := newTestCfg(fs)
+
+	for i := 0; i < len(configKeyValues); i += 2 {
+		cfg.Set(configKeyValues[i].(string), configKeyValues[i+1])
+	}
+	return newTestPathSpec(fs, cfg)
+}
+
+func newTestCfg(fs *hugofs.Fs) *viper.Viper {
+	v := viper.New()
+
+	v.SetFs(fs.Source)
+
+	return v
+
+}
+
+func newTestContentSpec() *ContentSpec {
+	v := viper.New()
+	return NewContentSpec(v)
+}