diff --git a/chords.cabal b/chords.cabal
index 1a9149c..a914980 100644
--- a/chords.cabal
+++ b/chords.cabal
@@ -4,7 +4,7 @@ cabal-version: 1.12
 --
 -- see: https://github.com/sol/hpack
 --
--- hash: ee4c89d7bed6b5301ea76804b74ab74db2265473402e362135317ea273e7ff33
+-- hash: f837b4f562ba53b2d2f26f2e7af5f96f55ac5c2865d732d975cabd9a52a90dc1
 
 name:           chords
 version:        0.1.0.0
@@ -51,8 +51,10 @@ library
   hs-source-dirs:
       src
   build-depends:
-      base >=4.7 && <5
+      QuickCheck
+    , base >=4.7 && <5
     , containers
+    , generic-random
     , parsec
   default-language: Haskell2010
 
@@ -64,9 +66,11 @@ executable chords-exe
       app
   ghc-options: -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      base >=4.7 && <5
+      QuickCheck
+    , base >=4.7 && <5
     , chords
     , containers
+    , generic-random
     , parsec
   default-language: Haskell2010
 
@@ -79,8 +83,10 @@ test-suite chords-test
       test
   ghc-options: -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      base >=4.7 && <5
+      QuickCheck
+    , base >=4.7 && <5
     , chords
     , containers
+    , generic-random
     , parsec
   default-language: Haskell2010
diff --git a/package.yaml b/package.yaml
index 49685bc..f56c417 100644
--- a/package.yaml
+++ b/package.yaml
@@ -23,6 +23,8 @@ dependencies:
 - base >= 4.7 && < 5
 - containers
 - parsec
+- generic-random
+- QuickCheck
 
 library:
   source-dirs: src
diff --git a/src/Base/Core/Quality/IQuality.hs b/src/Base/Core/Quality/IQuality.hs
index acd916e..6694b87 100644
--- a/src/Base/Core/Quality/IQuality.hs
+++ b/src/Base/Core/Quality/IQuality.hs
@@ -1,8 +1,13 @@
+{-# LANGUAGE DeriveGeneric #-}
 module Base.Core.Quality.IQuality
   ( Quality(..)
   , baseQuality
   ) where
 
+import GHC.Generics
+import Generic.Random
+import Test.QuickCheck
+
 import Common.Utils (modByFrom)
 
 data Quality
@@ -11,7 +16,10 @@ data Quality
  | Minor
  | Diminished Int
  | Augmented Int
- deriving Show
+ deriving (Show, Generic)
+
+instance Arbitrary Quality where
+  arbitrary = genericArbitrary uniform
 
 baseQuality :: Int -> Quality
 baseQuality n
diff --git a/src/Base/Interval.hs b/src/Base/Interval.hs
index a10dbb8..2d34f57 100644
--- a/src/Base/Interval.hs
+++ b/src/Base/Interval.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE DeriveGeneric #-}
 module Base.Interval
   ( Interval
   , getQuality
@@ -9,9 +10,14 @@ module Base.Interval
   , jumpIntervalFromNote
   , (|+|)
   , (|-|)
+  , propInvertSum
   , invert
   ) where
 
+import GHC.Generics
+import Generic.Random
+import Test.QuickCheck hiding (getSize)
+
 import Base.Core.Accidental
 import Base.Core.Note
 import Base.Core.Quality.IQuality
@@ -24,11 +30,23 @@ import Base.PitchClass
 
 import Common.Utils (modByFrom)
 
-import Data.Maybe (fromJust)
+import Data.Maybe (isJust, fromJust)
 
 data Interval = Interval { getQuality :: Quality
                          , getSize :: Int
-                         }
+                         } deriving (Generic)
+
+-- TODO: change to use a Maybe returning smart constructor when
+--       such a thing becomes avalible.
+--       The implemention of arbitrary will look something like:
+--         suchThatMap 
+--           (genericArbitrary uniform)
+--           (\(size, quality) -> intConstructor size quality)
+instance Arbitrary Interval where
+  arbitrary = suchThat (genericArbitrary uniform) (isJust . intervalToDistance)
+
+propInvertSum :: Interval -> Bool
+propInvertSum i = invert i |+| i == intervalFrom Perfect 1
 
 instance Eq Interval where
   int1 == int2 = intervalToDistance int1 == intervalToDistance int2