From e116cadb079566fc2e72746ebb7fb0d442d96838 Mon Sep 17 00:00:00 2001
From: Philipp Meier <philipp.meier@nubank.com.br>
Date: Thu, 7 Mar 2024 12:01:32 +0100
Subject: [PATCH] Add `returning` to support multiple results for function
 invocation.

This follows the suggestion in #10
---
 doc/documentation.md                  | 13 +++++++++++++
 src/mockfn/macros.cljc                | 10 ++++++++++
 test/mockfn/examples/basic_usage.cljc |  6 ++++++
 3 files changed, 29 insertions(+)

diff --git a/doc/documentation.md b/doc/documentation.md
index 0909696..ebba9d5 100644
--- a/doc/documentation.md
+++ b/doc/documentation.md
@@ -59,6 +59,19 @@ If you would like to call the value instead of returning it, use `mockfn.macros/
     (is (thrown? ExceptionInfo (one-fn)))))
 ```
 
+#### `returning`
+
+If you want to return different values for each invocation, use `mockfn.macros/returning`.
+Note that if the function will return `nil` afer all provided results are consumed.
+
+```clj
+(testing "providing - cause function non referential"
+    (mfn/providing [(one-fn :argument-1) (mfn/returning :result-1 :result-2 )]
+                   (is (= :result-1 (one-fn :argument-1)))
+                   (is (= :result-2 (one-fn :argument-1)))
+                   (is (nil? (one-fn :argument-1)))))
+```
+
 #### `fall-through`
 
 When mocking a function, it is sometimes useful to allow calls with specific
diff --git a/src/mockfn/macros.cljc b/src/mockfn/macros.cljc
index e1cc96c..b720ea5 100644
--- a/src/mockfn/macros.cljc
+++ b/src/mockfn/macros.cljc
@@ -32,3 +32,13 @@
          (doseq [mock# ~(into [] (keys specs#))]
            (mock/verify mock#))
          res#))))
+
+(defn returning
+  "Returns one value after the other. Used with `calling`"
+  [& values]
+  (let [stack (atom (into [] (reverse values)))
+        next (fn [_] (let [ret (peek @stack)]
+                       (when-not (empty? @stack)
+                         (swap! stack pop))
+                       ret))]
+    (calling next)))
diff --git a/test/mockfn/examples/basic_usage.cljc b/test/mockfn/examples/basic_usage.cljc
index bb47e69..7614ffb 100644
--- a/test/mockfn/examples/basic_usage.cljc
+++ b/test/mockfn/examples/basic_usage.cljc
@@ -25,6 +25,12 @@
       (is (thrown? ExceptionInfo (one-fn :argument-1)))
       (is (= :result-2 (one-fn :argument-2)))))
 
+  (testing "providing - cause function returns different results"
+    (mfn/providing [(one-fn :argument-1) (mfn/returning :result-1 :result-2 )]
+      (is (= :result-1 (one-fn :argument-1)))
+      (is (= :result-2 (one-fn :argument-1)))
+      (is (nil? (one-fn :argument-1)))))
+
   (testing "providing with more than one function"
     (mfn/providing [(one-fn :argument) :result-1
                     (other-fn :argument) :result-2]