unikernel/duniverse/dune_/doc/tutorials/developing-with-dune/unit-tests.md

@@ -0,0 +1,70 @@
+Unit Tests
+==========
+
+We're testing our calculator using cram tests, but in some cases, it can be more comfortable to use unit tests to test internal behaviors.
+
+In this chapter, we're going to extract the function that deals with conversion
+to floats and put it in a test harness.
+
+## Install Dependencies
+
+Run `opam install alcotest.1.7.0`.
+
+## Refactor
+
+Let's refactor our `eval_number_op` function in `lib/cli.ml` so that it uses the `as_float` function. Move `as_float` above it so that is can be used.
+
+```{code-block} ocaml
+let eval_number_op f_int f_float va vb =
+  match (va, vb) with
+  | VInt na, VInt nb -> VInt (f_int na nb)
+  | _ ->
+      let fa = as_float va in
+      let fb = as_float vb in
+      VFloat (f_float fa fb)
+```
+
+## Create a Test Suite
+
+We're first going to move our cram tests so that they can be in `test/cram/`,
+while our unit tests will be in `test/unit/`.
+
+Move the contents of the folder `test` into a fresh folder `test/cram/`.
+
+Create a folder `test/unit/`.
+
+Create `test/unit/dune` with the following contents:
+
+```dune
+(test
+ (name test_calc)
+ (libraries alcotest calc))
+```
+
+And `test/unit/test_calc.ml`:
+
+```ocaml
+open Calc
+
+let test_as_float =
+  let test ~name expression ~expected =
+    ( Printf.sprintf "as_float(%s)" name,
+      `Quick,
+      fun () ->
+        let got = Cli.as_float expression in
+        Alcotest.check
+          (Alcotest.float Stdlib.epsilon_float)
+          __LOC__ expected got )
+  in
+  [
+    test ~name:"int" (VInt 2) ~expected:2.;
+    test ~name:"float" (VFloat 3.5) ~expected:3.5;
+  ]
+
+let suite = [ ("as_float", test_as_float) ]
+
+let () = Alcotest.run __FILE__ suite
+```
+
+Now run `dune runtest`. In addition to the existing cram tests, this also runs
+unit tests.