Allow for provision of a Testcontainer instance

Testcontainers provides many different container implementations that
can be very useful. This simple change allows callers to provide their
own, premade container instance so consumers can flexibly choose their
container type. If no container instance is supplied, then
clj-test-containers falls back to its original behavior.

project.clj

@@ -9,5 +9,6 @@
   :plugins [[metosin/bat-test "0.4.4"]]
   :bat-test {:report [:pretty {:type :junit
                                :output-to "target/junit.xml"}]}
+  :profiles {:dev {:dependencies [[org.testcontainers/postgresql "1.14.3"]]}}
   :target-path "target/%s")
 

src/clj_test_containers/core.clj

@@ -13,8 +13,8 @@
 
 (defn create
   "Sets the properties for a testcontainer instance"
-  [{:keys [image-name exposed-ports env-vars command]}]
+  [{:keys [container image-name exposed-ports env-vars command]}]
-  (let [container (GenericContainer. image-name)]
+  (let [container (or container (GenericContainer. image-name))]
     (.setExposedPorts container (map int exposed-ports))
 
     (if (some? env-vars)

test/clj_test_containers/core_test.clj

@@ -1,6 +1,8 @@
 (ns clj-test-containers.core-test
   (:require [clojure.test :refer :all]
-            [clj-test-containers.core :refer :all]))
+            [clj-test-containers.core :refer :all])
+  (:import [org.testcontainers.containers
+            PostgreSQLContainer]))
 
 (deftest init-test
   (testing "Testing basic testcontainer generic image initialisation"
@@ -25,6 +27,16 @@
           result (execute-command! initialized-container ["whoami"])
           stopped-container (stop! container)]
       (is (= 0 (:exit-code result)))
+      (is (= "root\n" (:stdout result)))))
+
+  (testing "Executing a command in the running Docker container with a custom container"
+    (let [container (create {:container (PostgreSQLContainer. "postgres:12.2")
+                             :exposed-ports [5432]
+                             :env-vars {"POSTGRES_PASSWORD" "pw"}})
+          initialized-container (start! container)
+          result (execute-command! initialized-container ["whoami"])
+          stopped-container (stop! container)]
+      (is (= 0 (:exit-code result)))
       (is (= "root\n" (:stdout result))))))
 
 (deftest init-volume-test