Allow themes to define output formats, media types and params

This allows a `config.toml` (or `yaml`, ´yml`, or `json`)  in the theme to set:

1) `params` (but cannot override params in project. Will also get its own "namespace", i.e. `{{ .Site.Params.mytheme.my_param }}` will be the same as `{{ .Site.Params.my_param }}` providing that the main project does not define a param with that key.
2) `menu` -- but cannot redefine/add menus in the project. Must create its own menus with its own identifiers.
3) `languages` -- only `params` and `menu`. Same rules as above.
4) **new** `outputFormats`
5) **new** `mediaTypes`

This should help with the "theme portability" issue and people having to copy and paste lots of setting into their projects.

Fixes #4490

6 files changed, 536 insertions, 30 deletions

diff --git a/hugolib/case_insensitive_test.go b/hugolib/case_insensitive_test.go
index 680a701aa..52ef198a5 100644
--- a/hugolib/case_insensitive_test.go
+++ b/hugolib/case_insensitive_test.go
@@ -149,7 +149,7 @@ func TestCaseInsensitiveConfigurationVariations(t *testing.T) {
 
 	caseMixingTestsWriteCommonSources(t, mm)
 
-	cfg, err := LoadConfig(ConfigSourceDescriptor{Fs: mm})
+	cfg, _, err := LoadConfig(ConfigSourceDescriptor{Fs: mm, Filename: "config.toml"})
 	require.NoError(t, err)
 
 	fs := hugofs.NewFrom(mm, cfg)
diff --git a/hugolib/config.go b/hugolib/config.go
index e47e65435..6eca1a969 100644
--- a/hugolib/config.go
+++ b/hugolib/config.go
@@ -16,6 +16,7 @@ package hugolib
 import (
 	"errors"
 	"fmt"
+	"path/filepath"
 
 	"io"
 	"strings"
@@ -28,64 +29,91 @@ import (
 
 // ConfigSourceDescriptor describes where to find the config (e.g. config.toml etc.).
 type ConfigSourceDescriptor struct {
-	Fs   afero.Fs
-	Src  string
-	Name string
+	Fs afero.Fs
+
+	// Full path to the config file to use, i.e. /my/project/config.toml
+	Filename string
+
+	// The path to the directory to look for configuration. Is used if Filename is not
+	// set.
+	Path string
+
+	// The project's working dir. Is used to look for additional theme config.
+	WorkingDir string
 }
 
 func (d ConfigSourceDescriptor) configFilenames() []string {
-	return strings.Split(d.Name, ",")
+	return strings.Split(d.Filename, ",")
 }
 
 // LoadConfigDefault is a convenience method to load the default "config.toml" config.
 func LoadConfigDefault(fs afero.Fs) (*viper.Viper, error) {
-	return LoadConfig(ConfigSourceDescriptor{Fs: fs, Name: "config.toml"})
+	v, _, err := LoadConfig(ConfigSourceDescriptor{Fs: fs, Filename: "config.toml"})
+	return v, err
 }
 
 // LoadConfig loads Hugo configuration into a new Viper and then adds
 // a set of defaults.
-func LoadConfig(d ConfigSourceDescriptor) (*viper.Viper, error) {
+func LoadConfig(d ConfigSourceDescriptor) (*viper.Viper, []string, error) {
+	var configFiles []string
+
 	fs := d.Fs
 	v := viper.New()
 	v.SetFs(fs)
 
-	if d.Name == "" {
-		d.Name = "config.toml"
-	}
-
-	if d.Src == "" {
-		d.Src = "."
+	if d.Path == "" {
+		d.Path = "."
 	}
 
 	configFilenames := d.configFilenames()
 	v.AutomaticEnv()
 	v.SetEnvPrefix("hugo")
 	v.SetConfigFile(configFilenames[0])
-	v.AddConfigPath(d.Src)
+	v.AddConfigPath(d.Path)
 
 	err := v.ReadInConfig()
 	if err != nil {
 		if _, ok := err.(viper.ConfigParseError); ok {
-			return nil, err
+			return nil, configFiles, err
 		}
-		return nil, fmt.Errorf("Unable to locate Config file. Perhaps you need to create a new site.\n       Run `hugo help new` for details. (%s)\n", err)
+		return nil, configFiles, fmt.Errorf("Unable to locate Config file. Perhaps you need to create a new site.\n       Run `hugo help new` for details. (%s)\n", err)
+	}
+
+	if cf := v.ConfigFileUsed(); cf != "" {
+		configFiles = append(configFiles, cf)
 	}
+
 	for _, configFile := range configFilenames[1:] {
 		var r io.Reader
 		var err error
 		if r, err = fs.Open(configFile); err != nil {
-			return nil, fmt.Errorf("Unable to open Config file.\n (%s)\n", err)
+			return nil, configFiles, fmt.Errorf("Unable to open Config file.\n (%s)\n", err)
 		}
 		if err = v.MergeConfig(r); err != nil {
-			return nil, fmt.Errorf("Unable to parse/merge Config file (%s).\n (%s)\n", configFile, err)
+			return nil, configFiles, fmt.Errorf("Unable to parse/merge Config file (%s).\n (%s)\n", configFile, err)
 		}
+		configFiles = append(configFiles, configFile)
 	}
 
 	if err := loadDefaultSettingsFor(v); err != nil {
-		return v, err
+		return v, configFiles, err
 	}
 
-	return v, nil
+	themeConfigFile, err := loadThemeConfig(d, v)
+	if err != nil {
+		return v, configFiles, err
+	}
+
+	if themeConfigFile != "" {
+		configFiles = append(configFiles, themeConfigFile)
+	}
+
+	if err := loadLanguageSettings(v, nil); err != nil {
+		return v, configFiles, err
+	}
+
+	return v, configFiles, nil
+
 }
 
 func loadLanguageSettings(cfg config.Provider, oldLangs helpers.Languages) error {
@@ -201,6 +229,142 @@ func loadLanguageSettings(cfg config.Provider, oldLangs helpers.Languages) error
 	return nil
 }
 
+func loadThemeConfig(d ConfigSourceDescriptor, v1 *viper.Viper) (string, error) {
+
+	theme := v1.GetString("theme")
+	if theme == "" {
+		return "", nil
+	}
+
+	themesDir := helpers.AbsPathify(d.WorkingDir, v1.GetString("themesDir"))
+	configDir := filepath.Join(themesDir, theme)
+
+	var (
+		configPath string
+		exists     bool
+		err        error
+	)
+
+	// Viper supports more, but this is the sub-set supported by Hugo.
+	for _, configFormats := range []string{"toml", "yaml", "yml", "json"} {
+		configPath = filepath.Join(configDir, "config."+configFormats)
+		exists, err = helpers.Exists(configPath, d.Fs)
+		if err != nil {
+			return "", err
+		}
+		if exists {
+			break
+		}
+	}
+
+	if !exists {
+		// No theme config set.
+		return "", nil
+	}
+
+	v2 := viper.New()
+	v2.SetFs(d.Fs)
+	v2.AutomaticEnv()
+	v2.SetEnvPrefix("hugo")
+	v2.SetConfigFile(configPath)
+
+	err = v2.ReadInConfig()
+	if err != nil {
+		return "", err
+	}
+
+	const (
+		paramsKey    = "params"
+		languagesKey = "languages"
+		menuKey      = "menu"
+	)
+
+	for _, key := range []string{paramsKey, "outputformats", "mediatypes"} {
+		mergeStringMapKeepLeft("", key, v1, v2)
+	}
+
+	themeLower := strings.ToLower(theme)
+	themeParamsNamespace := paramsKey + "." + themeLower
+
+	// Set namespaced params
+	if v2.IsSet(paramsKey) && !v1.IsSet(themeParamsNamespace) {
+		// Set it in the default store to make sure it gets in the same or
+		// behind the others.
+		v1.SetDefault(themeParamsNamespace, v2.Get(paramsKey))
+	}
+
+	// Only add params and new menu entries, we do not add language definitions.
+	if v1.IsSet(languagesKey) && v2.IsSet(languagesKey) {
+		v1Langs := v1.GetStringMap(languagesKey)
+		for k, _ := range v1Langs {
+			langParamsKey := languagesKey + "." + k + "." + paramsKey
+			mergeStringMapKeepLeft(paramsKey, langParamsKey, v1, v2)
+		}
+		v2Langs := v2.GetStringMap(languagesKey)
+		for k, _ := range v2Langs {
+			if k == "" {
+				continue
+			}
+			langParamsKey := languagesKey + "." + k + "." + paramsKey
+			langParamsThemeNamespace := langParamsKey + "." + themeLower
+			// Set namespaced params
+			if v2.IsSet(langParamsKey) && !v1.IsSet(langParamsThemeNamespace) {
+				v1.SetDefault(langParamsThemeNamespace, v2.Get(langParamsKey))
+			}
+
+			langMenuKey := languagesKey + "." + k + "." + menuKey
+			if v2.IsSet(langMenuKey) {
+				// Only add if not in the main config.
+				v2menus := v2.GetStringMap(langMenuKey)
+				for k, v := range v2menus {
+					menuEntry := menuKey + "." + k
+					menuLangEntry := langMenuKey + "." + k
+					if !v1.IsSet(menuEntry) && !v1.IsSet(menuLangEntry) {
+						v1.Set(menuLangEntry, v)
+					}
+				}
+			}
+		}
+	}
+
+	// Add menu definitions from theme not found in project
+	if v2.IsSet("menu") {
+		v2menus := v2.GetStringMap(menuKey)
+		for k, v := range v2menus {
+			menuEntry := menuKey + "." + k
+			if !v1.IsSet(menuEntry) {
+				v1.SetDefault(menuEntry, v)
+			}
+		}
+	}
+
+	return v2.ConfigFileUsed(), nil
+
+}
+
+func mergeStringMapKeepLeft(rootKey, key string, v1, v2 *viper.Viper) {
+	if !v2.IsSet(key) {
+		return
+	}
+
+	if !v1.IsSet(key) && !(rootKey != "" && rootKey != key && v1.IsSet(rootKey)) {
+		v1.Set(key, v2.Get(key))
+		return
+	}
+
+	m1 := v1.GetStringMap(key)
+	m2 := v2.GetStringMap(key)
+
+	for k, v := range m2 {
+		if _, found := m1[k]; !found {
+			if rootKey != "" && v1.IsSet(rootKey+"."+k) {
+				continue
+			}
+			m1[k] = v
+		}
+	}
+}
+
 func loadDefaultSettingsFor(v *viper.Viper) error {
 
 	c, err := helpers.NewContentSpec(v)
@@ -281,5 +445,5 @@ lastmod = ["lastmod" ,":fileModTime", ":default"]
 
 	}
 
-	return loadLanguageSettings(v, nil)
+	return nil
 }
diff --git a/hugolib/config_test.go b/hugolib/config_test.go
index ec543d93d..441bcf541 100644
--- a/hugolib/config_test.go
+++ b/hugolib/config_test.go
@@ -17,13 +17,15 @@ import (
 	"testing"
 
 	"github.com/spf13/afero"
-	"github.com/stretchr/testify/assert"
+	"github.com/spf13/viper"
 	"github.com/stretchr/testify/require"
 )
 
 func TestLoadConfig(t *testing.T) {
 	t.Parallel()
 
+	assert := require.New(t)
+
 	// Add a random config variable for testing.
 	// side = page in Norwegian.
 	configContent := `
@@ -34,16 +36,19 @@ func TestLoadConfig(t *testing.T) {
 
 	writeToFs(t, mm, "hugo.toml", configContent)
 
-	cfg, err := LoadConfig(ConfigSourceDescriptor{Fs: mm, Name: "hugo.toml"})
+	cfg, _, err := LoadConfig(ConfigSourceDescriptor{Fs: mm, Filename: "hugo.toml"})
 	require.NoError(t, err)
 
-	assert.Equal(t, "side", cfg.GetString("paginatePath"))
+	assert.Equal("side", cfg.GetString("paginatePath"))
 	// default
-	assert.Equal(t, "layouts", cfg.GetString("layoutDir"))
+	assert.Equal("layouts", cfg.GetString("layoutDir"))
 }
+
 func TestLoadMultiConfig(t *testing.T) {
 	t.Parallel()
 
+	assert := require.New(t)
+
 	// Add a random config variable for testing.
 	// side = page in Norwegian.
 	configContentBase := `
@@ -59,9 +64,304 @@ func TestLoadMultiConfig(t *testing.T) {
 
 	writeToFs(t, mm, "override.toml", configContentSub)
 
-	cfg, err := LoadConfig(ConfigSourceDescriptor{Fs: mm, Name: "base.toml,override.toml"})
+	cfg, _, err := LoadConfig(ConfigSourceDescriptor{Fs: mm, Filename: "base.toml,override.toml"})
 	require.NoError(t, err)
 
-	assert.Equal(t, "top", cfg.GetString("paginatePath"))
-	assert.Equal(t, "same", cfg.GetString("DontChange"))
+	assert.Equal("top", cfg.GetString("paginatePath"))
+	assert.Equal("same", cfg.GetString("DontChange"))
+}
+
+func TestLoadConfigFromTheme(t *testing.T) {
+	t.Parallel()
+
+	assert := require.New(t)
+
+	mainConfigBasic := `
+theme = "test-theme"
+baseURL = "https://example.com/"
+
+`
+	mainConfig := `
+theme = "test-theme"
+baseURL = "https://example.com/"
+
+[frontmatter]
+date = ["date","publishDate"]
+
+[params]
+p1 = "p1 main"
+p2 = "p2 main"
+top = "top"
+
+[mediaTypes]
+[mediaTypes."text/m1"]
+suffix = "m1main"
+
+[outputFormats.o1]
+mediaType = "text/m1"
+baseName = "o1main"
+
+[languages]
+[languages.en]
+languageName = "English"
+[languages.en.params]
+pl1 = "p1-en-main"
+[languages.nb]
+languageName = "Norsk"
+[languages.nb.params]
+pl1 = "p1-nb-main"
+
+[[menu.main]]
+name = "menu-main-main"
+
+[[menu.top]]
+name = "menu-top-main"
+
+`
+
+	themeConfig := `
+baseURL = "http://bep.is/"
+
+# Can not be set in theme.
+[frontmatter]
+expiryDate = ["date"]
+
+[params]
+p1 = "p1 theme"
+p2 = "p2 theme"
+p3 = "p3 theme"
+
+[mediaTypes]
+[mediaTypes."text/m1"]
+suffix = "m1theme"
+[mediaTypes."text/m2"]
+suffix = "m2theme"
+
+[outputFormats.o1]
+mediaType = "text/m1"
+baseName = "o1theme"
+[outputFormats.o2]
+mediaType = "text/m2"
+baseName = "o2theme"
+
+[languages]
+[languages.en]
+languageName = "English2"
+[languages.en.params]
+pl1 = "p1-en-theme"
+pl2 = "p2-en-theme"
+[[languages.en.menu.main]]
+name   = "menu-lang-en-main"
+[[languages.en.menu.theme]]
+name   = "menu-lang-en-theme"
+[languages.nb]
+languageName = "Norsk2"
+[languages.nb.params]
+pl1 = "p1-nb-theme"
+pl2 = "p2-nb-theme"
+top = "top-nb-theme"
+[[languages.nb.menu.main]]
+name   = "menu-lang-nb-main"
+[[languages.nb.menu.theme]]
+name   = "menu-lang-nb-theme"
+[[languages.nb.menu.top]]
+name   = "menu-lang-nb-top"
+
+[[menu.main]]
+name = "menu-main-theme"
+
+[[menu.thememenu]]
+name = "menu-theme"
+
+`
+
+	b := newTestSitesBuilder(t)
+	b.WithConfigFile("toml", mainConfig).WithThemeConfigFile("toml", themeConfig)
+	b.CreateSites().Build(BuildCfg{})
+
+	got := b.Cfg.(*viper.Viper).AllSettings()
+
+	b.AssertObject(`
+map[string]interface {}{
+  "p1": "p1 main",
+  "p2": "p2 main",
+  "p3": "p3 theme",
+  "test-theme": map[string]interface {}{
+    "p1": "p1 theme",
+    "p2": "p2 theme",
+    "p3": "p3 theme",
+  },
+  "top": "top",
+}`, got["params"])
+
+	b.AssertObject(`
+map[string]interface {}{
+  "date": []interface {}{
+    "date",
+    "publishDate",
+  },
+}`, got["frontmatter"])
+
+	b.AssertObject(`
+map[string]interface {}{
+  "text/m1": map[string]interface {}{
+    "suffix": "m1main",
+  },
+  "text/m2": map[string]interface {}{
+    "suffix": "m2theme",
+  },
+}`, got["mediatypes"])
+
+	b.AssertObject(`
+map[string]interface {}{
+  "o1": map[string]interface {}{
+    "basename": "o1main",
+    "mediatype": Type{
+      MainType: "text",
+      SubType: "m1",
+      Suffix: "m1main",
+      Delimiter: ".",
+    },
+  },
+  "o2": map[string]interface {}{
+    "basename": "o2theme",
+    "mediatype": Type{
+      MainType: "text",
+      SubType: "m2",
+      Suffix: "m2theme",
+      Delimiter: ".",
+    },
+  },
+}`, got["outputformats"])
+
+	b.AssertObject(`map[string]interface {}{
+  "en": map[string]interface {}{
+    "languagename": "English",
+    "menu": map[string]interface {}{
+      "theme": []interface {}{
+        map[string]interface {}{
+          "name": "menu-lang-en-theme",
+        },
+      },
+    },
+    "params": map[string]interface {}{
+      "pl1": "p1-en-main",
+      "pl2": "p2-en-theme",
+      "test-theme": map[string]interface {}{
+        "pl1": "p1-en-theme",
+        "pl2": "p2-en-theme",
+      },
+    },
+  },
+  "nb": map[string]interface {}{
+    "languagename": "Norsk",
+    "menu": map[string]interface {}{
+      "theme": []interface {}{
+        map[string]interface {}{
+          "name": "menu-lang-nb-theme",
+        },
+      },
+    },
+    "params": map[string]interface {}{
+      "pl1": "p1-nb-main",
+      "pl2": "p2-nb-theme",
+      "test-theme": map[string]interface {}{
+        "pl1": "p1-nb-theme",
+        "pl2": "p2-nb-theme",
+        "top": "top-nb-theme",
+      },
+    },
+  },
+}
+`, got["languages"])
+
+	b.AssertObject(`
+map[string]interface {}{
+  "main": []interface {}{
+    map[string]interface {}{
+      "name": "menu-main-main",
+    },
+  },
+  "thememenu": []interface {}{
+    map[string]interface {}{
+      "name": "menu-theme",
+    },
+  },
+  "top": []interface {}{
+    map[string]interface {}{
+      "name": "menu-top-main",
+    },
+  },
+}
+`, got["menu"])
+
+	assert.Equal("https://example.com/", got["baseurl"])
+
+	if true {
+		return
+	}
+	// Test variants with only values from theme
+	b = newTestSitesBuilder(t)
+	b.WithConfigFile("toml", mainConfigBasic).WithThemeConfigFile("toml", themeConfig)
+	b.CreateSites().Build(BuildCfg{})
+
+	got = b.Cfg.(*viper.Viper).AllSettings()
+
+	b.AssertObject(`map[string]interface {}{
+  "p1": "p1 theme",
+  "p2": "p2 theme",
+  "p3": "p3 theme",
+  "test-theme": map[string]interface {}{
+    "p1": "p1 theme",
+    "p2": "p2 theme",
+    "p3": "p3 theme",
+  },
+}`, got["params"])
+
+	assert.Nil(got["languages"])
+	b.AssertObject(`
+map[string]interface {}{
+  "text/m1": map[string]interface {}{
+    "suffix": "m1theme",
+  },
+  "text/m2": map[string]interface {}{
+    "suffix": "m2theme",
+  },
+}`, got["mediatypes"])
+
+	b.AssertObject(`
+map[string]interface {}{
+  "o1": map[string]interface {}{
+    "basename": "o1theme",
+    "mediatype": Type{
+      MainType: "text",
+      SubType: "m1",
+      Suffix: "m1theme",
+      Delimiter: ".",
+    },
+  },
+  "o2": map[string]interface {}{
+    "basename": "o2theme",
+    "mediatype": Type{
+      MainType: "text",
+      SubType: "m2",
+      Suffix: "m2theme",
+      Delimiter: ".",
+    },
+  },
+}`, got["outputformats"])
+	b.AssertObject(`
+map[string]interface {}{
+  "main": []interface {}{
+    map[string]interface {}{
+      "name": "menu-main-theme",
+    },
+  },
+  "thememenu": []interface {}{
+    map[string]interface {}{
+      "name": "menu-theme",
+    },
+  },
+}`, got["menu"])
+
 }
diff --git a/hugolib/page_bundler_test.go b/hugolib/page_bundler_test.go
index bf79d2f86..572d84bcd 100644
--- a/hugolib/page_bundler_test.go
+++ b/hugolib/page_bundler_test.go
@@ -200,6 +200,7 @@ func TestPageBundlerSiteMultilingual(t *testing.T) {
 				cfg.Set("uglyURLs", ugly)
 
 				assert.NoError(loadDefaultSettingsFor(cfg))
+				assert.NoError(loadLanguageSettings(cfg, nil))
 				sites, err := NewHugoSites(deps.DepsCfg{Fs: fs, Cfg: cfg})
 				assert.NoError(err)
 				assert.Equal(2, len(sites.Sites))
@@ -264,6 +265,8 @@ func TestMultilingualDisableDefaultLanguage(t *testing.T) {
 	cfg.Set("disableLanguages", []string{"en"})
 
 	err := loadDefaultSettingsFor(cfg)
+	assert.NoError(err)
+	err = loadLanguageSettings(cfg, nil)
 	assert.Error(err)
 	assert.Contains(err.Error(), "cannot disable default language")
 }
diff --git a/hugolib/site.go b/hugolib/site.go
index 2e8898bd6..0ffe153e9 100644
--- a/hugolib/site.go
+++ b/hugolib/site.go
@@ -296,6 +296,7 @@ func NewSite(cfg deps.DepsCfg) (*Site, error) {
 // NewSiteDefaultLang creates a new site in the default language.
 // The site will have a template system loaded and ready to use.
 // Note: This is mainly used in single site tests.
+// TODO(bep) test refactor -- remove
 func NewSiteDefaultLang(withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
 	v := viper.New()
 	if err := loadDefaultSettingsFor(v); err != nil {
@@ -307,6 +308,7 @@ func NewSiteDefaultLang(withTemplate ...func(templ tpl.TemplateHandler) error) (
 // NewEnglishSite creates a new site in English language.
 // The site will have a template system loaded and ready to use.
 // Note: This is mainly used in single site tests.
+// TODO(bep) test refactor -- remove
 func NewEnglishSite(withTemplate ...func(templ tpl.TemplateHandler) error) (*Site, error) {
 	v := viper.New()
 	if err := loadDefaultSettingsFor(v); err != nil {
diff --git a/hugolib/testhelpers_test.go b/hugolib/testhelpers_test.go
index ab23b343c..1f22e428d 100644
--- a/hugolib/testhelpers_test.go
+++ b/hugolib/testhelpers_test.go
@@ -10,6 +10,8 @@ import (
 	"strings"
 	"text/template"
 
+	"github.com/sanity-io/litter"
+
 	jww "github.com/spf13/jwalterweatherman"
 
 	"github.com/gohugoio/hugo/config"
@@ -37,11 +39,15 @@ type sitesBuilder struct {
 	Fs  *hugofs.Fs
 	T   testing.TB
 
+	dumper litter.Options
+
 	// Aka the Hugo server mode.
 	running bool
 
 	H *HugoSites
 
+	theme string
+
 	// Default toml
 	configFormat string
 
@@ -63,7 +69,13 @@ func newTestSitesBuilder(t testing.TB) *sitesBuilder {
 	v := viper.New()
 	fs := hugofs.NewMem(v)
 
-	return &sitesBuilder{T: t, Fs: fs, configFormat: "toml"}
+	litterOptions := litter.Options{
+		HidePrivateFields: true,
+		StripPackageNames: true,
+		Separator:         " ",
+	}
+
+	return &sitesBuilder{T: t, Fs: fs, configFormat: "toml", dumper: litterOptions}
 }
 
 func (s *sitesBuilder) Running() *sitesBuilder {
@@ -97,6 +109,15 @@ func (s *sitesBuilder) WithConfigFile(format, conf string) *sitesBuilder {
 	return s
 }
 
+func (s *sitesBuilder) WithThemeConfigFile(format, conf string) *sitesBuilder {
+	if s.theme == "" {
+		s.theme = "test-theme"
+	}
+	filename := filepath.Join("themes", s.theme, "config."+format)
+	writeSource(s.T, s.Fs, filename, conf)
+	return s
+}
+
 func (s *sitesBuilder) WithSimpleConfigFile() *sitesBuilder {
 	var config = `
 baseURL = "http://example.com/"
@@ -229,10 +250,15 @@ func (s *sitesBuilder) CreateSites() *sitesBuilder {
 	s.writeFilePairs("i18n", s.i18nFilePairsAdded)
 
 	if s.Cfg == nil {
-		cfg, err := LoadConfig(ConfigSourceDescriptor{Fs: s.Fs.Source, Name: "config." + s.configFormat})
+		cfg, configFiles, err := LoadConfig(ConfigSourceDescriptor{Fs: s.Fs.Source, Filename: "config." + s.configFormat})
 		if err != nil {
 			s.Fatalf("Failed to load config: %s", err)
 		}
+		expectedConfigs := 1
+		if s.theme != "" {
+			expectedConfigs = 2
+		}
+		require.Equal(s.T, expectedConfigs, len(configFiles), fmt.Sprintf("Configs: %v", configFiles))
 		s.Cfg = cfg
 	}
 
@@ -345,6 +371,17 @@ func (s *sitesBuilder) AssertFileContent(filename string, matches ...string) {
 	}
 }
 
+func (s *sitesBuilder) AssertObject(expected string, object interface{}) {
+	got := s.dumper.Sdump(object)
+	expected = strings.TrimSpace(expected)
+
+	if expected != got {
+		fmt.Println(got)
+		diff := helpers.DiffStrings(expected, got)
+		s.Fatalf("diff:\n%s\nexpected\n%s\ngot\n%s", diff, expected, got)
+	}
+}
+
 func (s *sitesBuilder) AssertFileContentRe(filename string, matches ...string) {
 	content := readDestination(s.T, s.Fs, filename)
 	for _, match := range matches {