Add the single class loader.

src/main/java/space/kklochko/simple_jbdd/tests/loaders/SingleClassLoader.java

@@ -0,0 +1,26 @@
+package space.kklochko.simple_jbdd.tests.loaders;
+
+public class SingleClassLoader {
+    String className;
+
+    public SingleClassLoader(String className) {
+        setClassName(className);
+    }
+
+    public Class<?> load() {
+        try {
+            return Class.forName(getClassName());
+        } catch (ClassNotFoundException e) {
+            return null;
+        }
+    }
+
+    public String getClassName() {
+        return className;
+    }
+
+    public void setClassName(String className) {
+        this.className = className;
+    }
+}
+

src/test/groovy/space/kklochko/simple_jbdd/tests/loaders/IntegratedSingleClassLoader.groovy

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+package space.kklochko.simple_jbdd.tests.loaders
+
+import space.kklochko.simple_jbdd.test_examples.tests.SimpleThenTest
+import spock.lang.Narrative
+import spock.lang.Specification
+import spock.lang.Subject
+import spock.lang.Title
+
+@Narrative("""The loader must return a class or null, so
+those tests check if responses are right.
+""")
+@Title("Integrated tests for ClassLoader.")
+class IntegratedSingleClassLoader extends Specification {
+    def "The class has been run."() {
+        given: "I have a class loader"
+        @Subject
+        def loader = new SingleClassLoader(className);
+
+        when: "The class was loaded"
+        def aClass = loader.load()
+
+        then: "Checking that the test result is expected"
+        aClass == expectedClass
+
+        where: "Possible variants of tests"
+        className                                                       || expectedClass
+        "fourHundredFour"                                               || null
+        "space.kklochko.simple_jbdd.test_examples.tests.SimpleThenTest" || SimpleThenTest
+    }
+}
+