diff --git a/viper_test.go b/viper_test.go
index ed53272..afc63d1 100644
--- a/viper_test.go
+++ b/viper_test.go
@@ -18,6 +18,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/spf13/afero"
 	"github.com/spf13/cast"
 
 	"github.com/spf13/pflag"
@@ -847,6 +848,190 @@ func TestSub(t *testing.T) {
 	assert.Equal(t, (*Viper)(nil), subv)
 }
 
+var hclWriteExpected = []byte(`"foos" {
+  "foo" {
+    "key" 1
+  }
+
+  "foo" {
+    "key" 2
+  }
+
+  "foo" {
+    "key" 3
+  }
+
+  "foo" {
+    "key" 4
+  }
+}
+
+"id" "0001"
+
+"name" "Cake"
+
+"ppu" 0.55
+
+"type" "donut"`)
+
+func TestWriteConfigHCL(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.SetConfigName("c")
+	v.SetConfigType("hcl")
+	err := v.ReadConfig(bytes.NewBuffer(hclExample))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := v.WriteConfigAs("c.hcl"); err != nil {
+		t.Fatal(err)
+	}
+	read, err := afero.ReadFile(fs, "c.hcl")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, hclWriteExpected, read)
+}
+
+var jsonWriteExpected = []byte(`{
+  "batters": {
+    "batter": [
+      {
+        "type": "Regular"
+      },
+      {
+        "type": "Chocolate"
+      },
+      {
+        "type": "Blueberry"
+      },
+      {
+        "type": "Devil's Food"
+      }
+    ]
+  },
+  "id": "0001",
+  "name": "Cake",
+  "ppu": 0.55,
+  "type": "donut"
+}`)
+
+func TestWriteConfigJson(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.SetConfigName("c")
+	v.SetConfigType("json")
+	err := v.ReadConfig(bytes.NewBuffer(jsonExample))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := v.WriteConfigAs("c.json"); err != nil {
+		t.Fatal(err)
+	}
+	read, err := afero.ReadFile(fs, "c.json")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, jsonWriteExpected, read)
+}
+
+var propertiesWriteExpected = []byte(`p_id = 0001
+p_type = donut
+p_name = Cake
+p_ppu = 0.55
+p_batters.batter.type = Regular
+`)
+
+func TestWriteConfigProperties(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.SetConfigName("c")
+	v.SetConfigType("properties")
+	err := v.ReadConfig(bytes.NewBuffer(propertiesExample))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := v.WriteConfigAs("c.properties"); err != nil {
+		t.Fatal(err)
+	}
+	read, err := afero.ReadFile(fs, "c.properties")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, propertiesWriteExpected, read)
+}
+
+func TestWriteConfigTOML(t *testing.T) {
+	fs := afero.NewMemMapFs()
+	v := New()
+	v.SetFs(fs)
+	v.SetConfigName("c")
+	v.SetConfigType("toml")
+	err := v.ReadConfig(bytes.NewBuffer(tomlExample))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := v.WriteConfigAs("c.toml"); err != nil {
+		t.Fatal(err)
+	}
+
+	// The TOML String method does not order the contents.
+	// Therefore, we must read the generated file and compare the data.
+	v2 := New()
+	v2.SetFs(fs)
+	v2.SetConfigName("c")
+	v2.SetConfigType("toml")
+	v2.SetConfigFile("c.toml")
+	err = v2.ReadInConfig()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	assert.Equal(t, v.GetString("title"), v2.GetString("title"))
+	assert.Equal(t, v.GetString("owner.bio"), v2.GetString("owner.bio"))
+	assert.Equal(t, v.GetString("owner.dob"), v2.GetString("owner.dob"))
+	assert.Equal(t, v.GetString("owner.organization"), v2.GetString("owner.organization"))
+}
+
+var yamlWriteExpected = []byte(`age: 35
+beard: true
+clothing:
+  jacket: leather
+  pants:
+    size: large
+  trousers: denim
+eyes: brown
+hacker: true
+hobbies:
+- skateboarding
+- snowboarding
+- go
+name: steve
+`)
+
+func TestWriteConfigYAML(t *testing.T) {
+	v := New()
+	fs := afero.NewMemMapFs()
+	v.SetFs(fs)
+	v.SetConfigName("c")
+	v.SetConfigType("yaml")
+	err := v.ReadConfig(bytes.NewBuffer(yamlExample))
+	if err != nil {
+		t.Fatal(err)
+	}
+	if err := v.WriteConfigAs("c.yaml"); err != nil {
+		t.Fatal(err)
+	}
+	read, err := afero.ReadFile(fs, "c.yaml")
+	if err != nil {
+		t.Fatal(err)
+	}
+	assert.Equal(t, yamlWriteExpected, read)
+}
+
 var yamlMergeExampleTgt = []byte(`
 hello:
     pop: 37890