add JenkinsStepRule

test/groovy/util/JenkinsStepRule.groovy

@@ -0,0 +1,32 @@
+package util
+
+import com.lesfurets.jenkins.unit.BasePipelineTest
+
+import java.beans.Introspector
+
+import org.junit.rules.TestRule
+import org.junit.runner.Description
+import org.junit.runners.model.Statement
+
+class JenkinsStepRule implements TestRule {
+    final BasePipelineTest testInstance
+
+    def step
+
+    JenkinsStepRule(BasePipelineTest testInstance) {
+        this.testInstance = testInstance
+    }
+
+    @Override
+    Statement apply(Statement base, Description description) {
+        return new Statement() {
+            @Override
+            void evaluate() throws Throwable {
+                def testClassName = testInstance.getClass().getSimpleName()
+                def stepName = Introspector.decapitalize(testClassName.replaceAll('Test$', ''))
+                this.step = testInstance.loadScript("${stepName}.groovy")
+                base.evaluate()
+            }
+        }
+    }
+}