diff --git a/lab4/lab4.cabal b/lab4/lab4.cabal
index d953ad5..12e5dde 100644
--- a/lab4/lab4.cabal
+++ b/lab4/lab4.cabal
@@ -62,6 +62,7 @@ test-suite lab4-test
       test
   ghc-options: -Wall -Wcompat -Widentities -Wincomplete-record-updates -Wincomplete-uni-patterns -Wmissing-export-lists -Wmissing-home-modules -Wpartial-fields -Wredundant-constraints -threaded -rtsopts -with-rtsopts=-N
   build-depends:
-      base >=4.7 && <5
+      QuickCheck
+    , base >=4.7 && <5
     , lab4
   default-language: Haskell2010
diff --git a/lab4/package.yaml b/lab4/package.yaml
index 7484a48..2429c0f 100644
--- a/lab4/package.yaml
+++ b/lab4/package.yaml
@@ -57,3 +57,4 @@ tests:
     - -with-rtsopts=-N
     dependencies:
     - lab4
+    - QuickCheck
diff --git a/lab4/test/Spec.hs b/lab4/test/Spec.hs
index cd4753f..360ec28 100644
--- a/lab4/test/Spec.hs
+++ b/lab4/test/Spec.hs
@@ -1,2 +1,20 @@
+import Test.QuickCheck
+import Lib (isCongruent)
+
+propCongruentDifference :: Int -> Int -> Int -> Property
+propCongruentDifference a b m =
+  m /= 0 ==> isCongruent a b m == ((a - b) `mod` m == 0)
+
+propCongruentSymmetric :: Int -> Int -> Int -> Property
+propCongruentSymmetric a b m =
+  m /= 0 ==> isCongruent a b m == isCongruent b a m
+
+propCongruentEqualNumbers :: Int -> Int -> Property
+propCongruentEqualNumbers a m =
+  m /= 0 ==> isCongruent a a m == True
+
 main :: IO ()
-main = putStrLn "Test suite not yet implemented"
+main = do
+  quickCheck propCongruentDifference
+  quickCheck propCongruentSymmetric
+  quickCheck propCongruentEqualNumbers