Create admin user only if it does not yet exist

Fixes #28

src/main/java/catering/users/UserDataInitializer.java

@@ -1,6 +1,7 @@
 package catering.users;
 
 import org.salespointframework.core.DataInitializer;
+import org.salespointframework.useraccount.UserAccountManagement;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.stereotype.Component;
@@ -13,15 +14,19 @@ class UserDataInitializer implements DataInitializer {
 
 	private static final Logger LOG = LoggerFactory.getLogger(UserDataInitializer.class);
 	private final UserManagement userManagement;
+	private final UserAccountManagement userAccountManagement;
 
-	UserDataInitializer(UserManagement userManagement) {
+	UserDataInitializer(UserManagement userManagement, UserAccountManagement userAccountManagement) {
 		Assert.notNull(userManagement, "UserRepository must not be null!");
 		this.userManagement = userManagement;
+		this.userAccountManagement = userAccountManagement;
 	}
 
 	@Override
 	public void initialize() {
-		LOG.info("Creating default user.");
-		userManagement.createAdmin("admin", "admin", "admin");
+		if (userAccountManagement.findByUsername("admin").isEmpty()) {
+			LOG.info("Creating default user.");
+			userManagement.createAdmin("admin", "admin", "admin");
+		}
 	}
 }

src/test/java/catering/users/UserDataInitializerIntegrationTests.java

@@ -0,0 +1,42 @@
+package catering.users;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.salespointframework.useraccount.UserAccount.UserAccountIdentifier;
+import org.salespointframework.useraccount.UserAccountManagement;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest
+class UserDataInitializerIntegrationTests {
+	@Autowired
+	UserManagement userManagement;
+	@Autowired
+	UserAccountManagement userAccountManagement;
+
+	UserDataInitializer userDataInitializer;
+
+	@BeforeEach
+	void init() {
+		userDataInitializer = new UserDataInitializer(userManagement, userAccountManagement);
+	}
+
+	/**
+	 * Test if the administrator’s account is only created once.
+	 *
+	 * If the admin is either replaced or attempted to be created a second time,
+	 * the test will fail or throw an {@link IllegalArgumentException} respectively.
+	 *
+	 * @throws Exception
+	 */
+	@Test
+	void onlyCreateAdminOnce() throws Exception {
+		UserAccountIdentifier idBefore = userAccountManagement.findByUsername("admin").get().getId();
+		userDataInitializer.initialize();
+		UserAccountIdentifier idAfter = userAccountManagement.findByUsername("admin").get().getId();
+
+		assertThat(idAfter).isEqualTo(idBefore);
+	}
+}