Add DeployerWithPostTester interface

This allows the deployer to define after-test behavior based on the results of the test.

Unfortunately PostTest can't be wrapped in writer.WrapStep because PostTest has an error parameter but WrapStep expects `func() error`

pkg/app/app.go

@@ -140,11 +140,22 @@ func RealMain(opts types.Options, d types.Deployer, tester types.Tester) (result
 
 		}
 		test.SetEnv(envsForTester...)
+
+		var testErr error
 		if !opts.SkipTestJUnitReport() {
-			return writer.WrapStep("Test", test.Run)
+			testErr = writer.WrapStep("Test", test.Run)
+		} else {
+			testErr = test.Run()
 		}
-		return test.Run()
-	}
 
+		if dWithPostTester, ok := d.(types.DeployerWithPostTester); ok {
+			if err := dWithPostTester.PostTest(testErr); err != nil {
+				return err
+			}
+		}
+		if testErr != nil {
+			return testErr
+		}
+	}
 	return nil
 }

pkg/types/types.go

@@ -103,6 +103,16 @@ type DeployerWithProvider interface {
 	Provider() string
 }
 
+// DeployerWithPostTester adds the ability to define after-test behavior
+// based on the results of the test.
+type DeployerWithPostTester interface {
+	Deployer
+
+	// PostTest runs after the tester completes.
+	// testErr is the error returned from the tester's Run()
+	PostTest(testErr error) error
+}
+
 // Tester defines the "interface" between kubetest2 and a tester
 // The tester is executed as a separate binary during the Test() phase
 type Tester struct {