diff --git a/src/propeller/push/instructions/string.cljc b/src/propeller/push/instructions/string.cljc
index 7d88e03..445373b 100755
--- a/src/propeller/push/instructions/string.cljc
+++ b/src/propeller/push/instructions/string.cljc
@@ -38,7 +38,7 @@
   :string_contains
   ^{:stacks #{:boolean :string}}
   (fn [state]
-    (make-instruction state string/includes? [:string :string] :boolean)))
+    (make-instruction state #(string/includes? %2 %1) [:string :string] :boolean)))
 
 ;; Pushes TRUE if the top CHAR is contained in the top STRING, and FALSE
 ;; otherwise
diff --git a/test/propeller/push/instructions/string_spec.clj b/test/propeller/push/instructions/string_spec.clj
new file mode 100644
index 0000000..50ea2de
--- /dev/null
+++ b/test/propeller/push/instructions/string_spec.clj
@@ -0,0 +1,116 @@
+(ns propeller.push.instructions.string-spec
+  (:require
+   [clojure.string :as string]
+   [clojure.test.check.generators :as gen]
+   [clojure.test.check.properties :as prop]
+   [clojure.test.check.clojure-test :as ct :refer [defspec]]
+   [propeller.push.state :as state]
+   [propeller.push.core :as core]
+   [propeller.push.instructions.string :as string-instructions]))
+
+
+;; string/butlast
+
+(defn check-butlast
+  [value]
+  (let [start-state (state/push-to-stack state/empty-state
+                                         :string
+                                         value)
+        end-state ((:string_butlast @core/instruction-table) start-state)
+        expected-result (apply str (butlast value))]
+    (= expected-result
+       (state/peek-stack end-state :string))))
+
+(defspec butlast-spec 100
+  (prop/for-all [str gen/string] 
+                (check-butlast str)))
+
+
+;; string/concat
+
+(defn check-concat
+  [value1 value2]
+  (let [start-state (-> state/empty-state
+                        (state/push-to-stack :string value1)
+                        (state/push-to-stack :string value2))
+        end-state ((:string_concat @core/instruction-table) start-state)
+        expected-result (str value1 value2)]
+    (= expected-result
+       (state/peek-stack end-state :string))))
+  
+(defspec concat-spec 100
+  (prop/for-all [str1 gen/string
+                 str2 gen/string]
+                (check-concat str1 str2)))
+
+
+;; string/conj-char
+
+(defn check-conj-char
+  [value char]
+  (let [start-state (-> state/empty-state
+                        (state/push-to-stack :string value)
+                        (state/push-to-stack :char char))
+        end-state ((:string_conj_char @core/instruction-table) start-state)
+        expected-result (str value char)]
+    (= expected-result
+       (state/peek-stack end-state :string))))
+
+(defspec conj-char-spec 100
+  (prop/for-all [str gen/string
+                 char gen/char]
+                (check-conj-char str char)))
+
+
+;; string/contains
+
+(defn check-contains
+  [value1 value2]
+  (let [start-state (-> state/empty-state
+                        (state/push-to-stack :string value1)
+                        (state/push-to-stack :string value2))
+        end-state ((:string_contains @core/instruction-table) start-state)
+        expected-result (string/includes? value2 value1)]
+    (= expected-result
+       (state/peek-stack end-state :boolean))))
+
+(defspec contains-spec 100
+  (prop/for-all [str1 gen/string
+                 str2 gen/string]
+                (check-contains str1 str2)))
+
+
+;; string/contains-char
+
+(defn check-contains-char
+  [value char]
+  (let [start-state (-> state/empty-state
+                        (state/push-to-stack :string value)
+                        (state/push-to-stack :char char))
+        end-state ((:string_contains_char @core/instruction-table) start-state)
+        expected-result (string/includes? value (str char))]
+    (= expected-result
+       (state/peek-stack end-state :boolean))))
+
+(defspec contains-char-spec 100
+  (prop/for-all [str gen/string
+                 char gen/char]
+                (check-contains-char str char)))
+
+
+;; string/drop
+
+(defn check-drop
+  [value n]
+  (let [start-state (-> state/empty-state
+                        (state/push-to-stack :string value)
+                        (state/push-to-stack :integer n))
+        end-state ((:string_drop @core/instruction-table) start-state)
+        expected-result (apply str (drop n value))]
+    (= expected-result
+       (state/peek-stack end-state :string))))
+
+(defspec drop-spec 100
+  (prop/for-all [str gen/string
+                 int gen/small-integer]
+                (check-drop str int)))
\ No newline at end of file