diff --git a/.drone.yml b/.drone.yml
index bc490cf..4020516 100644
--- a/.drone.yml
+++ b/.drone.yml
@@ -1,11 +1,13 @@
 ---
 kind: pipeline
 type: docker
-name: build
+name: test-and-lint
 
 steps:
   - name: notify-start
     image: pztrn/discordrone
+    when:
+      instance: ci.dev.pztrn.name
     settings:
       webhook_id:
         from_secret: discord_webhook_id
@@ -16,16 +18,25 @@ steps:
   - name: lint
     image: golangci/golangci-lint:latest
     environment:
-      CGO_ENABLED: 0
+      CGO_ENABLED: "0"
     commands:
       - golangci-lint run
     depends_on:
       - notify-start
 
-  - name: test-1.13
-    image: golang:1.13.5-alpine
+  - name: test-1.14
+    image: golang:1.14.4-alpine
     environment:
-      CGO_ENABLED: 0
+      CGO_ENABLED: "0"
+    commands:
+      - go test -cover -test.v .
+    depends_on:
+      - notify-start
+
+  - name: test-1.13
+    image: golang:1.13.12-alpine
+    environment:
+      CGO_ENABLED: "0"
     commands:
       - go test -cover -test.v .
     depends_on:
@@ -33,6 +44,7 @@ steps:
 
   - name: notify-end
     when:
+      instance: ci.dev.pztrn.name
       status:
         - success
         - failure
@@ -51,3 +63,4 @@ steps:
     depends_on:
       - lint
       - test-1.13
+      - test-1.14
diff --git a/.golangci.yml b/.golangci.yml
index 549ef2f..413fda7 100644
--- a/.golangci.yml
+++ b/.golangci.yml
@@ -15,4 +15,9 @@ linters-settings:
     line-length: 420
   gocyclo:
     min-complexity: 40
-  
\ No newline at end of file
+issues:
+  exclude-rules:
+    # We do not want to enforce black-box testing.
+    - path: flagger_test.go
+      linters:
+        - testpackage
diff --git a/errors.go b/errors.go
new file mode 100644
index 0000000..53f3bf0
--- /dev/null
+++ b/errors.go
@@ -0,0 +1,36 @@
+// Flagger - arbitrary CLI flags parser.
+//
+// Copyright (c) 2017-2019, Stanislav N. aka pztrn.
+//
+// Permission is hereby granted, free of charge, to any person obtaining
+// a copy of this software and associated documentation files (the
+// "Software"), to deal in the Software without restriction, including
+// without limitation the rights to use, copy, modify, merge, publish,
+// distribute, sublicense, and/or sell copies of the Software, and to
+// permit persons to whom the Software is furnished to do so, subject
+// to the following conditions:
+//
+// The above copyright notice and this permission notice shall be
+// included in all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+// IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+// CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+// TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE
+// OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
+package flagger
+
+import "errors"
+
+var (
+	// ErrFlagAlreadyAdded appears when trying to register a flag with
+	// an already used name (field Name).
+	ErrFlagAlreadyAdded = errors.New("flag already added")
+
+	// ErrNoSuchFlag appears when trying to request a value for a flag
+	// that wasn't registered.
+	ErrNoSuchFlag = errors.New("no such flag")
+)
diff --git a/example/main.go b/example/main.go
index 8c40729..1a868a2 100644
--- a/example/main.go
+++ b/example/main.go
@@ -1,7 +1,7 @@
 package main
 
 import (
-	"gitlab.com/pztrn/flagger"
+	"go.dev.pztrn.name/flagger"
 )
 
 var f *flagger.Flagger
diff --git a/flagger.go b/flagger.go
index 00c4554..125492a 100644
--- a/flagger.go
+++ b/flagger.go
@@ -25,7 +25,7 @@ package flagger
 
 import (
 	// stdlib
-	"errors"
+
 	"flag"
 	"os"
 )
@@ -52,7 +52,7 @@ type Flagger struct {
 func (f *Flagger) AddFlag(flag *Flag) error {
 	_, present := f.flags[flag.Name]
 	if present {
-		return errors.New("Cannot add flag '" + flag.Name + "' - already added!")
+		return ErrFlagAlreadyAdded
 	}
 
 	f.flags[flag.Name] = flag
@@ -66,7 +66,7 @@ func (f *Flagger) AddFlag(flag *Flag) error {
 func (f *Flagger) GetBoolValue(name string) (bool, error) {
 	fl, present := f.flagsBool[name]
 	if !present {
-		return false, errors.New("No such flag: " + name)
+		return false, ErrNoSuchFlag
 	}
 
 	return (*fl), nil
@@ -77,7 +77,7 @@ func (f *Flagger) GetBoolValue(name string) (bool, error) {
 func (f *Flagger) GetIntValue(name string) (int, error) {
 	fl, present := f.flagsInt[name]
 	if !present {
-		return 0, errors.New("No such flag: " + name)
+		return 0, ErrNoSuchFlag
 	}
 
 	return (*fl), nil
@@ -88,7 +88,7 @@ func (f *Flagger) GetIntValue(name string) (int, error) {
 func (f *Flagger) GetStringValue(name string) (string, error) {
 	fl, present := f.flagsString[name]
 	if !present {
-		return "", errors.New("No such flag: " + name)
+		return "", ErrNoSuchFlag
 	}
 
 	return (*fl), nil
diff --git a/go.mod b/go.mod
index b0667dc..af721b9 100644
--- a/go.mod
+++ b/go.mod
@@ -3,5 +3,6 @@ module go.dev.pztrn.name/flagger
 go 1.13
 
 require (
-	github.com/stretchr/testify v1.2.2
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/stretchr/testify v1.6.1
 )
diff --git a/go.sum b/go.sum
index b7a9475..0f20d4a 100644
--- a/go.sum
+++ b/go.sum
@@ -1,8 +1,13 @@
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
 github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/stretchr/testify v1.2.2 h1:bSDNvY7ZPG5RlJ8otE/7V6gMiyenm9RtJ7IUVIAoJ1w=
-github.com/stretchr/testify v1.2.2/go.mod h1:a8OnRcib4nhh0OaRAV+Yts87kKdq0PP7pXfy6kDkUVs=
-gitlab.com/pztrn/flagger v0.0.0-20191015160147-a9ca273d8b73 h1:3wo+sJrNguob5mLnQQmH2/Rh2oCuEhIplgWpAMutFzY=
-gitlab.com/pztrn/flagger v0.0.0-20191015160147-a9ca273d8b73/go.mod h1:I+FxZN2hnd4iELlBFizaDD4QJy92x6Ky4+76U7L3gBQ=
+github.com/stretchr/objx v0.1.0 h1:4G4v2dO3VZwixGIRoQ5Lfboy6nUhCyYzaqnIAPPhYs4=
+github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
+github.com/stretchr/testify v1.6.1 h1:hDPOHmpOpP40lSULcqw7IrRb/u7w6RpDC9399XyoNd0=
+github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c h1:dUUwHk2QECo/6vqA44rthZ8ie2QXMNeKRTHCNY2nXvo=
+gopkg.in/yaml.v3 v3.0.0-20200313102051-9f266ea9e77c/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=