Allow to customize an existing application (for tests, mocking, etc.)

Fixes gh-44

Author: sdeleuze

jafu/src/main/java/org/springframework/fu/jafu/JafuApplication.java

@@ -19,6 +19,8 @@ public abstract class JafuApplication {
 
 	private final ApplicationContextInitializer<GenericApplicationContext> initializer;
 
+	private ApplicationContextInitializer<GenericApplicationContext> customizer;
+
 	protected JafuApplication(ApplicationContextInitializer<GenericApplicationContext> initializer) {
 		this.initializer = initializer;
 	}
@@ -79,10 +81,16 @@ protected void load(ApplicationContext context, Object[] sources) {
 			app.setAdditionalProfiles(Arrays.stream(profiles.split(",")).map(it -> it.trim()).toArray(String[]::new));
 		}
 		app.addInitializers(this.initializer);
+		if (this.customizer != null) app.addInitializers(this.customizer);
 		System.setProperty("spring.backgroundpreinitializer.ignore", "true");
 		return app.run(args);
 	}
 
+	public JafuApplication customize(Consumer<ApplicationDsl> customizer) {
+		this.customizer = new ApplicationDsl(customizer);
+		return this;
+	}
+
 	protected abstract void initializeWebApplicationContext(SpringApplication app);
 
 }

jafu/src/test/java/org/springframework/fu/jafu/ApplicationDslTests.java

@@ -51,9 +51,30 @@ void applicationProperties() {
 		context.close();
 	}
 
+	@Test
+	void replaceBeanOfExistingApplication() {
+		var app = application(a -> a.beans(b -> b.bean(Bar.class, () -> new Bar("original"))));
+		var context = app.customize(a -> a.beans(b -> b.bean(Bar.class, () -> new Bar("customized"), c -> c.setPrimary(true)))).run();
+		assertEquals("customized", context.getBean(Bar.class).value);
+		context.close();
+	}
+
 
 	static class Foo {}
 
+	static class Bar {
+
+		private final String value;
+
+		public Bar(String value) {
+			this.value = value;
+		}
+
+		public String getValue() {
+			return value;
+		}
+	}
+
 	static class City {
 
 		private String name;

kofu/build.gradle.kts

@@ -40,6 +40,7 @@ dependencies {
 	testRuntimeOnly("de.flapdoodle.embed:de.flapdoodle.embed.mongo")
 	testImplementation(project(":coroutines:data-mongodb"))
 	testImplementation(project(":coroutines:webflux"))
+	testImplementation("io.mockk:mockk:1.9")
 }
 
 tasks.withType<DokkaTask> {

kofu/src/main/kotlin/org/springframework/fu/kofu/KofuApplication.kt

@@ -14,6 +14,8 @@ import org.springframework.context.support.GenericApplicationContext
  */
 abstract class KofuApplication(private val initializer: ApplicationContextInitializer<GenericApplicationContext>) {
 
+    private var customizer: (ApplicationDsl.() -> Unit)? = null
+
     /**
      * Run the current application
      * @param profiles [ApplicationContext] profiles separated by commas.
@@ -31,10 +33,15 @@ abstract class KofuApplication(private val initializer: ApplicationContextInitia
             app.setAdditionalProfiles(*profiles.split(",").map { it.trim() }.toTypedArray())
         }
         app.addInitializers(initializer)
+        if (customizer != null) app.addInitializers(ApplicationDsl(customizer!!))
         System.setProperty("spring.backgroundpreinitializer.ignore", "true")
         return app.run(*args)
     }
 
+    fun customize(customizer: ApplicationDsl.() -> Unit) {
+        this.customizer = customizer
+    }
+
     protected abstract fun initializeWebApplicationContext(app: SpringApplication)
 
 }

kofu/src/test/kotlin/org/springframework/fu/kofu/ApplicationDslTests.kt

@@ -16,6 +16,8 @@
 
 package org.springframework.fu.kofu
 
+import io.mockk.every
+import io.mockk.mockk
 import org.junit.jupiter.api.Assertions.assertEquals
 import org.junit.jupiter.api.Assertions.assertFalse
 import org.junit.jupiter.api.Test
@@ -44,7 +46,7 @@ class ApplicationDslTests {
 	fun `Create an application with a custom bean`() {
 		val app = application {
 			beans {
-				bean<Foo>()
+				bean<Foo>(isPrimary = true)
 			}
 		}
 		with(app.run()) {
@@ -82,8 +84,31 @@ class ApplicationDslTests {
 		}
 	}
 
+	@Test
+	fun `Mock a bean of an existing application`() {
+		val app = application {
+			beans {
+				bean { Bar("original") }
+			}
+		}
+		app.customize {
+			beans {
+				bean(isPrimary = true) {
+					mockk<Bar>().apply {
+						every { value } returns "customized"
+					}
+				}
+			}
+		}
+		with(app.run()) {
+			assertEquals("customized", getBean<Bar>().value)
+			close()
+		}
+	}
+
 
 	class Foo
+	class Bar(val value: String)
 
 	// Switch to data classes when https://github.com/spring-projects/spring-boot/issues/8762 will be fixed
 	class City {