diff --git a/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_4_calling_functions.res b/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_4_calling_functions.res
new file mode 100644
index 00000000..d595f35a
--- /dev/null
+++ b/packages/squiggle-lang/__tests__/ReducerProject/ReducerProject_tutorial_4_calling_functions.res
@@ -0,0 +1,39 @@
+@@warning("-44")
+module InternalExpressionValue = ReducerInterface_InternalExpressionValue
+module Project = ForTS_ReducerProject
+module Bindings = Reducer_Bindings
+
+open Jest
+open Expect
+open Expect.Operators
+
+describe("ReducerProject Tutorial", () => {
+  /* Let's build a project to provide a function. */
+  /* But we will call that function on an array of user input. */
+  let project = Project.createProject()
+  Project.setSource(project, "library", "double(x) = x * 2")
+  /* userCode is not here yet but its dependency is fixed. So we can set it once and for all */
+  Project.setContinues(project, "userCode", ["library"])
+
+  let userValues = [1, 2, 3, 4, 5]
+
+  let userResults = Belt.Array.map(userValues, aUserValue => {
+    let userCode = `double(${aUserValue->Js.Int.toString})`
+    /* Put the constructed source in the project */
+    /* We have already set that it depends on "library" */
+    Project.setSource(project, "userCode", userCode)
+    /* Run the project */
+    Project.runAll(project)
+    /* Get the result */
+    Project.getResult(project, "userCode")
+    /* I have to remind you that the "library" is run only once and for all.
+     The library is not run for each user value. */
+  })
+
+  test("userResults", () => {
+    let userResultsAsString = Belt.Array.map(userResults, aResult =>
+      aResult->InternalExpressionValue.toStringOptionResult
+    )
+    userResultsAsString->expect == ["Ok(2)", "Ok(4)", "Ok(6)", "Ok(8)", "Ok(10)"]
+  })
+})