Add alive? function to expose java.lang.Process::isAlive (#92)

src/babashka/process.cljc

@@ -592,3 +592,8 @@
               (tokenize cmd))
         cmd (into cmd args)]
     (check (process prev cmd (merge default-shell-opts opts)))))
+
+(defn alive?
+  "Returns `true` if the process is still running and false otherwise."
+  [p]
+  (.isAlive ^java.lang.Process (:proc p)))

test/babashka/process_test.cljc

@@ -285,6 +285,13 @@
 
 (jdk9+)
 
+(deftest alive-lives
+  (let [{:keys [in] :as res} (process '[cat])]
+    (is (true? (p/alive? res)))
+    (.close in)
+    @res
+    (is (false? (p/alive? res)))))
+
 ;;;; Windows tests
 ;;;; Run with clojure -M:test -i windows