diff --git a/opbtest/opbtestmockable.py b/opbtest/opbtestmockable.py
index 0f1ab14..1fffac4 100644
--- a/opbtest/opbtestmockable.py
+++ b/opbtest/opbtestmockable.py
@@ -3,6 +3,7 @@ class OpbTestMockable():
         self.case = case
         self.filename = filename
         self.prepender = []
+        self.replacers = {}
         self.inputs = {}
         self.proctotest = ""
         self.appender = ["\nopbtestquitfn: output sD, FF\n"]
@@ -18,6 +19,13 @@ class OpbTestMockable():
             self.prepender.append("load " + key + ", " + str(val) + "\n")
         return self
 
+    def replace(self, statement1, statement2):
+        self.replacers[statement1] = statement2
+        return self
+
+    def mockproc(self, procname):
+        return self.replace("call " + procname, "load s0, s0")
+
     def mockinput(self, port, value):
         self.inputs[port] = value
         return self
@@ -62,10 +70,24 @@ class OpbTestMockable():
                     newdata.append(line)
             return newdata
 
+        def setupreplaces(data):
+            newdata = []
+            for line in data:
+                found = False
+                for key, value in self.replacers.items():
+                    if line.upper().replace(" ", "").startswith(key.upper().replace(" ", "")):
+                        newdata.append(value)
+                        found = True
+                if found is False:
+                    newdata.append(line)
+            return newdata
+
         if len(self.proctotest) > 0:
             data = setupproc(data)
         if len(self.inputs) > 0:
             data = setupinputs(data)
+        if len(self.replacers) > 0:
+            data = setupreplaces(data)
 
         firstjump = findlinebetween(data, "jump", "jump")
 
diff --git a/test/mocks.psm4 b/test/mocks.psm4
new file mode 100644
index 0000000..f22ad5c
--- /dev/null
+++ b/test/mocks.psm4
@@ -0,0 +1,9 @@
+jump main
+
+proc myproc(s1 is bla) {
+    load s0, 11
+}
+
+main:
+    call myproc
+    output sD, FF
\ No newline at end of file
diff --git a/test/test_mocks.py b/test/test_mocks.py
new file mode 100644
index 0000000..5582d29
--- /dev/null
+++ b/test/test_mocks.py
@@ -0,0 +1,16 @@
+from opbtest import OpbTestCase
+
+
+class TestMocks(OpbTestCase):
+
+    def test_mockproc_replaces_call_statements_with_dummies(self):
+        assert_that = self.load_file("mocks.psm4").mockproc("myproc").execute()
+        assert_that.reg("s0").contains(0)
+
+    def test_replace_replaces_statement_with_given(self):
+        assert_that = self.load_file("mocks.psm4").replace("load s0, 11", "load s0, 3").execute()
+        assert_that.reg("s0").contains(3)
+
+    def test_do_not_replace_anything(self):
+        assert_that = self.load_file("mocks.psm4").execute()
+        assert_that.reg("s0").contains(11)