Add common_test namespace with map-diff function

The map-diff function searches two collections with the same structure
for equal keywords with differing values and returns the diff as a map.

src/main/cljc/dda/c4k_common/common_test.cljc

@@ -0,0 +1,26 @@
+(ns dda.c4k-common.common-test)
+
+; Heavily assumes c1 and c2 have an identical structure but maybe different values
+; This function finds the diff of two nested maps/vectors
+(defn map-diff
+  ([c1 c2]
+   (into {}
+         (cond (or (map? c1) (vector? c1))
+               (map
+                #(if (= (% c1) (% c2))
+                   nil
+                   (let [c1-value (% c1)
+                         c2-value (% c2)
+                         key-name (name %)]
+                     (cond
+                       (map? c1-value) (map-diff c1-value c2-value)
+                       (vector? c1-value) (map-diff c1-value c2-value key-name)
+                       :else {(keyword (str key-name "-c1")) c1-value
+                              (keyword (str key-name "-c2")) c2-value})))
+                (keys c1)))))
+  ([c1 c2 last-name]
+   (first (for [x c1 y c2] (cond
+                             (map? x) (map-diff x y)
+                             (vector? x) (map-diff x y last-name)
+                             :else {(keyword (str last-name "-c1")) x
+                                    (keyword (str last-name "-c2")) y})))))