From e7b4c2c63762a5933e4c385f6b67a0885d6f2bf8 Mon Sep 17 00:00:00 2001
From: Jay <jayzawrotny@gmail.com>
Date: Wed, 23 Feb 2022 07:37:57 -0500
Subject: [PATCH] Added with-redefs macro and test

---
 src/promesa/core.cljc             | 22 +++++++++++++++++++++-
 test/promesa/tests/core_test.cljc | 10 ++++++++++
 2 files changed, 31 insertions(+), 1 deletion(-)

diff --git a/src/promesa/core.cljc b/src/promesa/core.cljc
index eda4646..5618fe0 100644
--- a/src/promesa/core.cljc
+++ b/src/promesa/core.cljc
@@ -26,7 +26,7 @@
   (:refer-clojure :exclude [delay spread promise
                             await map mapcat run!
                             future let loop recur
-                            -> ->> as->])
+                            -> ->> as-> with-redefs])
   (:require
    [promesa.protocols :as pt]
    [clojure.core :as c]
@@ -535,3 +535,23 @@
      ~(if (empty? forms)
         name
         (last forms))))
+
+(defmacro with-redefs
+  "Like clojure.core/with-redefs, but it will handle promises in
+   body and wait until they resolve or reject before restoring the
+   bindings. Useful for mocking async APIs."
+  [bindings & body]
+  (c/let [names (take-nth 2 bindings)
+          vals (take-nth 2 (drop 1 bindings))
+          orig-val-syms (map (comp gensym #(str % "-orig-val__") name) names)
+          temp-val-syms (map (comp gensym #(str % "-temp-val__") name) names)
+          binds (map vector names temp-val-syms)
+          resets (reverse (map vector names orig-val-syms))
+          bind-value (fn [[k v]] (list 'alter-var-root (list 'var k) (list 'constantly v)))]
+    `(c/let [~@(interleave orig-val-syms names)
+           ~@(interleave temp-val-syms vals)]
+       ~@(map bind-value binds)
+       (c/-> (do! ~@body)
+             (finally
+               (fn []
+                 ~@(map bind-value resets)))))))
diff --git a/test/promesa/tests/core_test.cljc b/test/promesa/tests/core_test.cljc
index 6d9fb01..0282c87 100644
--- a/test/promesa/tests/core_test.cljc
+++ b/test/promesa/tests/core_test.cljc
@@ -458,3 +458,13 @@
         test #(p/then p1 (fn [res] (t/is (= res 8))))]
     #?(:cljs (t/async done (p/do! (test) (done)))
        :clj @(test))))
+
+(t/deftest with-redefs-macro
+  (let [a-fn (fn [] (p/resolved "original"))
+        a-var :original
+        p1   (p/with-redefs [a-fn (fn [] (p/resolved "mocked"))
+                             a-var :mocked]
+               (p/then (a-fn) #(vector % a-var)))
+        test #(p/then p1 (fn [res] (t/is (= res ["mocked" :mocked]))))]
+    #?(:cljs (t/async done (p/do! (test) (done)))
+       :clj @(test))))