For #42:

As per PR review:
* Inversion of control: the condition class itself now performs the
  actual test

Author: llorllale

src/test/java/com/amihaiemil/docker/mock/AssertRequest.java

@@ -152,9 +152,7 @@ public <T> T execute(final HttpHost target, final HttpRequest request,
      */
     private void check(final HttpRequest request) {
         this.conditions.forEach(cond -> {
-            if (!cond.test().test(request)) {
-                Assert.fail(cond.msg());
-            }
+            cond.test(request);
         });
     }
 }

src/test/java/com/amihaiemil/docker/mock/Condition.java

@@ -27,6 +27,7 @@
 
 import java.util.function.Predicate;
 import org.apache.http.HttpRequest;
+import org.junit.Assert;
 
 /**
  * Condition that an {@link HttpRequest} must satisfy.
@@ -57,20 +58,14 @@ public Condition(final String msg, final Predicate<HttpRequest> test) {
     }
 
     /**
-     * The failure message.
-     * 
-     * @return The failure message.
-     */
-    public String msg() {
-        return this.msg;
-    }
-
-    /**
-     * The test for the http request.
+     * Tests the request.
      * 
-     * @return The test for the http request.
+     * @param request The request to test.
+     * @throws AssertionError if the request does not satisfy this condition
      */
-    public Predicate<HttpRequest> test() {
-        return this.test;
+    public void test(final HttpRequest request) {
+        if (!this.test.test(request)) {
+            Assert.fail(this.msg);
+        }
     }
 }