first working example with use case and persistence adapter

.gitignore

@@ -0,0 +1,30 @@
+HELP.md
+.gradle
+/build/
+!gradle/wrapper/gradle-wrapper.jar
+
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+/out/
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+
+### VS Code ###
+.vscode/

build.gradle

@@ -0,0 +1,38 @@
+plugins {
+    id 'org.springframework.boot' version '2.1.4.RELEASE'
+    id 'java'
+}
+
+apply plugin: 'io.spring.dependency-management'
+
+group = 'io.reflectoring'
+version = '0.0.1-SNAPSHOT'
+sourceCompatibility = '1.8'
+
+configurations {
+    compileOnly {
+        extendsFrom annotationProcessor
+    }
+}
+
+repositories {
+    mavenCentral()
+}
+
+dependencies {
+    implementation 'org.springframework.boot:spring-boot-starter-web'
+    implementation 'org.springframework.boot:spring-boot-starter-data-jdbc'
+    compileOnly 'org.projectlombok:lombok'
+    runtimeOnly 'com.h2database:h2'
+    annotationProcessor 'org.projectlombok:lombok'
+    testImplementation('org.springframework.boot:spring-boot-starter-test') {
+        exclude group: 'junit' // excluding junit 4
+    }
+    testImplementation 'org.junit.jupiter:junit-jupiter-engine:5.0.1'
+    testImplementation 'org.mockito:mockito-junit-jupiter:2.23.0'
+    testImplementation 'com.tngtech.archunit:archunit:0.9.3'
+}
+
+test {
+    useJUnitPlatform()
+}

gradlew

@@ -0,0 +1,172 @@
+#!/usr/bin/env sh
+
+##############################################################################
+##
+##  Gradle start up script for UN*X
+##
+##############################################################################
+
+# Attempt to set APP_HOME
+# Resolve links: $0 may be a link
+PRG="$0"
+# Need this for relative symlinks.
+while [ -h "$PRG" ] ; do
+    ls=`ls -ld "$PRG"`
+    link=`expr "$ls" : '.*-> \(.*\)$'`
+    if expr "$link" : '/.*' > /dev/null; then
+        PRG="$link"
+    else
+        PRG=`dirname "$PRG"`"/$link"
+    fi
+done
+SAVED="`pwd`"
+cd "`dirname \"$PRG\"`/" >/dev/null
+APP_HOME="`pwd -P`"
+cd "$SAVED" >/dev/null
+
+APP_NAME="Gradle"
+APP_BASE_NAME=`basename "$0"`
+
+# Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+DEFAULT_JVM_OPTS='"-Xmx64m"'
+
+# Use the maximum available, or set MAX_FD != -1 to use that value.
+MAX_FD="maximum"
+
+warn () {
+    echo "$*"
+}
+
+die () {
+    echo
+    echo "$*"
+    echo
+    exit 1
+}
+
+# OS specific support (must be 'true' or 'false').
+cygwin=false
+msys=false
+darwin=false
+nonstop=false
+case "`uname`" in
+  CYGWIN* )
+    cygwin=true
+    ;;
+  Darwin* )
+    darwin=true
+    ;;
+  MINGW* )
+    msys=true
+    ;;
+  NONSTOP* )
+    nonstop=true
+    ;;
+esac
+
+CLASSPATH=$APP_HOME/gradle/wrapper/gradle-wrapper.jar
+
+# Determine the Java command to use to start the JVM.
+if [ -n "$JAVA_HOME" ] ; then
+    if [ -x "$JAVA_HOME/jre/sh/java" ] ; then
+        # IBM's JDK on AIX uses strange locations for the executables
+        JAVACMD="$JAVA_HOME/jre/sh/java"
+    else
+        JAVACMD="$JAVA_HOME/bin/java"
+    fi
+    if [ ! -x "$JAVACMD" ] ; then
+        die "ERROR: JAVA_HOME is set to an invalid directory: $JAVA_HOME
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+    fi
+else
+    JAVACMD="java"
+    which java >/dev/null 2>&1 || die "ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+
+Please set the JAVA_HOME variable in your environment to match the
+location of your Java installation."
+fi
+
+# Increase the maximum file descriptors if we can.
+if [ "$cygwin" = "false" -a "$darwin" = "false" -a "$nonstop" = "false" ] ; then
+    MAX_FD_LIMIT=`ulimit -H -n`
+    if [ $? -eq 0 ] ; then
+        if [ "$MAX_FD" = "maximum" -o "$MAX_FD" = "max" ] ; then
+            MAX_FD="$MAX_FD_LIMIT"
+        fi
+        ulimit -n $MAX_FD
+        if [ $? -ne 0 ] ; then
+            warn "Could not set maximum file descriptor limit: $MAX_FD"
+        fi
+    else
+        warn "Could not query maximum file descriptor limit: $MAX_FD_LIMIT"
+    fi
+fi
+
+# For Darwin, add options to specify how the application appears in the dock
+if $darwin; then
+    GRADLE_OPTS="$GRADLE_OPTS \"-Xdock:name=$APP_NAME\" \"-Xdock:icon=$APP_HOME/media/gradle.icns\""
+fi
+
+# For Cygwin, switch paths to Windows format before running java
+if $cygwin ; then
+    APP_HOME=`cygpath --path --mixed "$APP_HOME"`
+    CLASSPATH=`cygpath --path --mixed "$CLASSPATH"`
+    JAVACMD=`cygpath --unix "$JAVACMD"`
+
+    # We build the pattern for arguments to be converted via cygpath
+    ROOTDIRSRAW=`find -L / -maxdepth 1 -mindepth 1 -type d 2>/dev/null`
+    SEP=""
+    for dir in $ROOTDIRSRAW ; do
+        ROOTDIRS="$ROOTDIRS$SEP$dir"
+        SEP="|"
+    done
+    OURCYGPATTERN="(^($ROOTDIRS))"
+    # Add a user-defined pattern to the cygpath arguments
+    if [ "$GRADLE_CYGPATTERN" != "" ] ; then
+        OURCYGPATTERN="$OURCYGPATTERN|($GRADLE_CYGPATTERN)"
+    fi
+    # Now convert the arguments - kludge to limit ourselves to /bin/sh
+    i=0
+    for arg in "$@" ; do
+        CHECK=`echo "$arg"|egrep -c "$OURCYGPATTERN" -`
+        CHECK2=`echo "$arg"|egrep -c "^-"`                                 ### Determine if an option
+
+        if [ $CHECK -ne 0 ] && [ $CHECK2 -eq 0 ] ; then                    ### Added a condition
+            eval `echo args$i`=`cygpath --path --ignore --mixed "$arg"`
+        else
+            eval `echo args$i`="\"$arg\""
+        fi
+        i=$((i+1))
+    done
+    case $i in
+        (0) set -- ;;
+        (1) set -- "$args0" ;;
+        (2) set -- "$args0" "$args1" ;;
+        (3) set -- "$args0" "$args1" "$args2" ;;
+        (4) set -- "$args0" "$args1" "$args2" "$args3" ;;
+        (5) set -- "$args0" "$args1" "$args2" "$args3" "$args4" ;;
+        (6) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" ;;
+        (7) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" ;;
+        (8) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" ;;
+        (9) set -- "$args0" "$args1" "$args2" "$args3" "$args4" "$args5" "$args6" "$args7" "$args8" ;;
+    esac
+fi
+
+# Escape application args
+save () {
+    for i do printf %s\\n "$i" | sed "s/'/'\\\\''/g;1s/^/'/;\$s/\$/' \\\\/" ; done
+    echo " "
+}
+APP_ARGS=$(save "$@")
+
+# Collect all arguments for the java command, following the shell quoting and substitution rules
+eval set -- $DEFAULT_JVM_OPTS $JAVA_OPTS $GRADLE_OPTS "\"-Dorg.gradle.appname=$APP_BASE_NAME\"" -classpath "\"$CLASSPATH\"" org.gradle.wrapper.GradleWrapperMain "$APP_ARGS"
+
+# by default we should be in the correct project dir, but when run from Finder on Mac, the cwd is wrong
+if [ "$(uname)" = "Darwin" ] && [ "$HOME" = "$PWD" ]; then
+  cd "$(dirname "$0")"
+fi
+
+exec "$JAVACMD" "$@"

gradlew.bat

@@ -0,0 +1,84 @@
+@if "%DEBUG%" == "" @echo off
+@rem ##########################################################################
+@rem
+@rem  Gradle startup script for Windows
+@rem
+@rem ##########################################################################
+
+@rem Set local scope for the variables with windows NT shell
+if "%OS%"=="Windows_NT" setlocal
+
+set DIRNAME=%~dp0
+if "%DIRNAME%" == "" set DIRNAME=.
+set APP_BASE_NAME=%~n0
+set APP_HOME=%DIRNAME%
+
+@rem Add default JVM options here. You can also use JAVA_OPTS and GRADLE_OPTS to pass JVM options to this script.
+set DEFAULT_JVM_OPTS="-Xmx64m"
+
+@rem Find java.exe
+if defined JAVA_HOME goto findJavaFromJavaHome
+
+set JAVA_EXE=java.exe
+%JAVA_EXE% -version >NUL 2>&1
+if "%ERRORLEVEL%" == "0" goto init
+
+echo.
+echo ERROR: JAVA_HOME is not set and no 'java' command could be found in your PATH.
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:findJavaFromJavaHome
+set JAVA_HOME=%JAVA_HOME:"=%
+set JAVA_EXE=%JAVA_HOME%/bin/java.exe
+
+if exist "%JAVA_EXE%" goto init
+
+echo.
+echo ERROR: JAVA_HOME is set to an invalid directory: %JAVA_HOME%
+echo.
+echo Please set the JAVA_HOME variable in your environment to match the
+echo location of your Java installation.
+
+goto fail
+
+:init
+@rem Get command-line arguments, handling Windows variants
+
+if not "%OS%" == "Windows_NT" goto win9xME_args
+
+:win9xME_args
+@rem Slurp the command line arguments.
+set CMD_LINE_ARGS=
+set _SKIP=2
+
+:win9xME_args_slurp
+if "x%~1" == "x" goto execute
+
+set CMD_LINE_ARGS=%*
+
+:execute
+@rem Setup the command line
+
+set CLASSPATH=%APP_HOME%\gradle\wrapper\gradle-wrapper.jar
+
+@rem Execute Gradle
+"%JAVA_EXE%" %DEFAULT_JVM_OPTS% %JAVA_OPTS% %GRADLE_OPTS% "-Dorg.gradle.appname=%APP_BASE_NAME%" -classpath "%CLASSPATH%" org.gradle.wrapper.GradleWrapperMain %CMD_LINE_ARGS%
+
+:end
+@rem End local scope for the variables with windows NT shell
+if "%ERRORLEVEL%"=="0" goto mainEnd
+
+:fail
+rem Set variable GRADLE_EXIT_CONSOLE if you need the _script_ return code instead of
+rem the _cmd.exe /c_ return code!
+if  not "" == "%GRADLE_EXIT_CONSOLE%" exit 1
+exit /b 1
+
+:mainEnd
+if "%OS%"=="Windows_NT" endlocal
+
+:omega

settings.gradle

@@ -0,0 +1,6 @@
+pluginManagement {
+	repositories {
+		gradlePluginPortal()
+	}
+}
+rootProject.name = 'clean-architecture-example'

src/main/java/io/reflectoring/reviewapp/BookReviewerApplication.java

@@ -0,0 +1,14 @@
+package io.reflectoring.reviewapp;
+
+import org.springframework.boot.SpringApplication;
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.data.jdbc.repository.config.EnableJdbcRepositories;
+
+@SpringBootApplication
+public class BookReviewerApplication {
+
+  public static void main(String[] args) {
+    SpringApplication.run(BookReviewerApplication.class, args);
+  }
+
+}

src/main/java/io/reflectoring/reviewapp/adapter/persistence/AuthorPersistenceAdapter.java

@@ -0,0 +1,21 @@
+package io.reflectoring.reviewapp.adapter.persistence;
+
+import io.reflectoring.reviewapp.application.port.out.FindAuthorByIdPort;
+import io.reflectoring.reviewapp.domain.Author;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+
+@Component
+@RequiredArgsConstructor
+class AuthorPersistenceAdapter implements FindAuthorByIdPort {
+
+  private final AuthorRepository authorRepository;
+
+  @Override
+  public Author findAuthorById(Long authorId) {
+    return authorRepository.findById(authorId)
+            .orElseThrow(() -> new AuthorNotFoundException(authorId));
+  }
+
+
+}

src/main/java/io/reflectoring/reviewapp/adapter/persistence/AuthorRepository.java

@@ -0,0 +1,7 @@
+package io.reflectoring.reviewapp.adapter.persistence;
+
+import io.reflectoring.reviewapp.domain.Author;
+import org.springframework.data.repository.CrudRepository;
+
+public interface AuthorRepository extends CrudRepository<Author, Long> {
+}

src/main/java/io/reflectoring/reviewapp/adapter/persistence/BookPersistenceAdapter.java

@@ -0,0 +1,26 @@
+package io.reflectoring.reviewapp.adapter.persistence;
+
+import io.reflectoring.reviewapp.application.port.out.FindBookByTitlePort;
+import io.reflectoring.reviewapp.application.port.out.PersistBookPort;
+import io.reflectoring.reviewapp.domain.Book;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+
+import java.util.Optional;
+
+@Component
+@RequiredArgsConstructor
+class BookPersistenceAdapter implements FindBookByTitlePort, PersistBookPort {
+
+  private final BookRepository bookRepository;
+
+  @Override
+  public Optional<Book> findBookByTitle(String title) {
+    return bookRepository.findByTitle(title);
+  }
+
+  @Override
+  public Book saveBook(Book book) {
+    return bookRepository.save(book);
+  }
+}

src/main/java/io/reflectoring/reviewapp/adapter/persistence/BookRepository.java

@@ -0,0 +1,15 @@
+package io.reflectoring.reviewapp.adapter.persistence;
+
+import io.reflectoring.reviewapp.domain.Book;
+import org.springframework.data.jdbc.repository.query.Query;
+import org.springframework.data.repository.CrudRepository;
+import org.springframework.data.repository.query.Param;
+
+import java.util.Optional;
+
+interface BookRepository extends CrudRepository<Book, Long> {
+
+  @Query("select b.* from Book b where b.title = :title")
+  Optional<Book> findByTitle(@Param("title") String title);
+
+}

src/main/java/io/reflectoring/reviewapp/adapter/persistence/PersistenceAdapterConfiguration.java

@@ -0,0 +1,13 @@
+package io.reflectoring.reviewapp.adapter.persistence;
+
+import org.springframework.context.annotation.ComponentScan;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.data.jdbc.repository.config.EnableJdbcRepositories;
+import org.springframework.data.jdbc.repository.config.JdbcConfiguration;
+
+@Configuration
+@EnableJdbcRepositories
+@ComponentScan
+class PersistenceAdapterConfiguration extends JdbcConfiguration {
+
+}

src/main/java/io/reflectoring/reviewapp/application/port/in/RegisterBookUseCase.java

@@ -0,0 +1,41 @@
+package io.reflectoring.reviewapp.application.port.in;
+
+import io.reflectoring.reviewapp.common.SelfValidating;
+import lombok.Getter;
+
+import javax.validation.constraints.NotEmpty;
+import javax.validation.constraints.NotNull;
+
+public interface RegisterBookUseCase {
+
+  /**
+   * Allows an author to register a new book to be reviewed.
+   */
+  void registerBook(RegisterBookCommand command) throws NonUniqueBookTitleException;
+
+
+  @Getter
+  final class RegisterBookCommand extends SelfValidating<RegisterBookCommand> {
+
+    @NotEmpty
+    private final String bookTitle;
+
+    @NotNull
+    private final Long authorId;
+
+    public RegisterBookCommand(String bookTitle, Long authorId) {
+      this.bookTitle = bookTitle;
+      this.authorId = authorId;
+      validateSelf();
+    }
+  }
+
+  final class NonUniqueBookTitleException extends RuntimeException {
+
+    public NonUniqueBookTitleException(String bookTitle) {
+      super(String.format("A book title must be unique (book title in question: '%s').", bookTitle));
+    }
+
+  }
+
+}

src/main/java/io/reflectoring/reviewapp/application/port/out/FindAuthorByIdPort.java

@@ -0,0 +1,15 @@
+package io.reflectoring.reviewapp.application.port.out;
+
+import io.reflectoring.reviewapp.domain.Author;
+
+public interface FindAuthorByIdPort {
+
+  Author findAuthorById(Long authorId) throws AuthorNotFoundException;
+
+  class AuthorNotFoundException extends RuntimeException {
+    public AuthorNotFoundException(Long authorId) {
+      super(String.format("Author with ID '%d' does not exist!", authorId));
+    }
+  }
+
+}

src/main/java/io/reflectoring/reviewapp/application/port/out/FindBookByTitlePort.java

@@ -0,0 +1,11 @@
+package io.reflectoring.reviewapp.application.port.out;
+
+import io.reflectoring.reviewapp.domain.Book;
+
+import java.util.Optional;
+
+public interface FindBookByTitlePort {
+
+  Optional<Book> findBookByTitle(String title);
+
+}

src/main/java/io/reflectoring/reviewapp/application/port/out/PersistBookPort.java

@@ -0,0 +1,9 @@
+package io.reflectoring.reviewapp.application.port.out;
+
+import io.reflectoring.reviewapp.domain.Book;
+
+public interface PersistBookPort {
+
+  Book saveBook(Book book);
+
+}

src/main/java/io/reflectoring/reviewapp/application/service/RegisterBookService.java

@@ -0,0 +1,44 @@
+package io.reflectoring.reviewapp.application.service;
+
+import io.reflectoring.reviewapp.application.port.in.RegisterBookUseCase;
+import io.reflectoring.reviewapp.application.port.out.FindAuthorByIdPort;
+import io.reflectoring.reviewapp.application.port.out.FindBookByTitlePort;
+import io.reflectoring.reviewapp.application.port.out.PersistBookPort;
+import io.reflectoring.reviewapp.domain.Author;
+import io.reflectoring.reviewapp.domain.Book;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+
+@Service
+@RequiredArgsConstructor
+public class RegisterBookService implements RegisterBookUseCase {
+
+  private final FindAuthorByIdPort findAuthorByIdPort;
+  private final FindBookByTitlePort findBookByTitlePort;
+  private final PersistBookPort saveBookPort;
+
+  @Override
+  public void registerBook(RegisterBookCommand command) {
+
+    Author author = findAuthorByIdPort.findAuthorById(command.getAuthorId());
+
+    requireUniqueTitle(command.getBookTitle());
+    requireAuthorHasPremiumAccount(author);
+
+    // more business validations ...
+
+    Book book = new Book(null, command.getBookTitle(), author.getId());
+    saveBookPort.saveBook(book);
+  }
+
+  private void requireAuthorHasPremiumAccount(Author author) {
+    // some business validation ...
+  }
+
+  private void requireUniqueTitle(String bookTitle) {
+    if (findBookByTitlePort.findBookByTitle(bookTitle).isPresent()) {
+      throw new NonUniqueBookTitleException(bookTitle);
+    }
+  }
+
+}

src/main/java/io/reflectoring/reviewapp/common/SelfValidating.java

@@ -0,0 +1,29 @@
+package io.reflectoring.reviewapp.common;
+
+import javax.validation.ConstraintViolation;
+import javax.validation.ConstraintViolationException;
+import javax.validation.Validation;
+import javax.validation.Validator;
+import javax.validation.ValidatorFactory;
+import java.util.Set;
+
+public abstract class SelfValidating<T> {
+
+  private Validator validator;
+
+  public SelfValidating() {
+    ValidatorFactory factory = Validation.buildDefaultValidatorFactory();
+    validator = factory.getValidator();
+  }
+
+  /**
+   * Evaluates all Bean Validations on the attributes of this
+   * instance.
+   */
+  protected void validateSelf() {
+    Set<ConstraintViolation<T>> violations = validator.validate((T) this);
+    if (!violations.isEmpty()) {
+      throw new ConstraintViolationException(violations);
+    }
+  }
+}

src/main/java/io/reflectoring/reviewapp/domain/Author.java

@@ -0,0 +1,16 @@
+package io.reflectoring.reviewapp.domain;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import org.springframework.data.annotation.Id;
+import org.springframework.data.relational.core.mapping.Column;
+
+@Getter
+@AllArgsConstructor
+public class Author {
+
+  @Id
+  private Long id;
+  private String name;
+
+}

src/main/java/io/reflectoring/reviewapp/domain/Book.java

@@ -0,0 +1,18 @@
+package io.reflectoring.reviewapp.domain;
+
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import org.springframework.data.annotation.Id;
+
+@Getter
+@AllArgsConstructor
+public class Book {
+
+  @Id
+  private Long id;
+  private String title;
+  private Long authorId;
+
+  // imagine some insanely complex business logic methods ...
+
+}

src/main/resources/application.properties

@@ -0,0 +1 @@
+logging.level.org.springframework.jdbc.core.JdbcTemplate=DEBUG

src/main/resources/io/reflectoring/reviewapp/adapter/persistence/single-book-reset.sql

@@ -0,0 +1,2 @@
+DELETE FROM AUTHOR WHERE ID = 42;
+DELETE FROM BOOK WHERE ID = 1;

src/main/resources/io/reflectoring/reviewapp/adapter/persistence/single-book.sql

@@ -0,0 +1,5 @@
+INSERT INTO AUTHOR (ID, NAME)
+VALUES (42, 'Tom');
+
+INSERT INTO BOOK (ID, TITLE, AUTHOR_ID)
+VALUES (1, 'Get Your Hands Dirty on Clean Architecture', 42);

src/main/resources/schema.sql

@@ -0,0 +1,12 @@
+CREATE TABLE BOOK
+(
+    id        BIGINT auto_increment NOT NULL,
+    title     VARCHAR(50)           NOT NULL,
+    author_id BIGINT                NOT NULL
+);
+
+CREATE TABLE AUTHOR
+(
+    id          BIGINT auto_increment NOT NULL,
+    name VARCHAR(50)           NOT NULL
+);

src/test/java/io/reflectoring/reviewapp/BookReviewerApplicationTests.java

@@ -0,0 +1,16 @@
+package io.reflectoring.reviewapp;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.junit.jupiter.SpringExtension;
+
+@ExtendWith(SpringExtension.class)
+@SpringBootTest
+class BookReviewerApplicationTests {
+
+	@Test
+	void contextLoads() {
+	}
+
+}

src/test/java/io/reflectoring/reviewapp/adapter/persistence/BookPersistenceAdapterTest.java

@@ -0,0 +1,43 @@
+package io.reflectoring.reviewapp.adapter.persistence;
+
+import io.reflectoring.reviewapp.domain.Book;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.jdbc.Sql;
+import org.springframework.test.context.jdbc.Sql.ExecutionPhase;
+import org.springframework.test.context.jdbc.SqlGroup;
+
+import java.util.Optional;
+
+import static org.assertj.core.api.Assertions.*;
+
+@SpringBootTest
+class BookPersistenceAdapterTest {
+
+  @Autowired
+  private BookPersistenceAdapter bookPersistenceAdapter;
+
+  @Autowired
+  private BookRepository bookRepository;
+
+  @Test
+  @SqlGroup({
+          @Sql(scripts = "single-book.sql", executionPhase = ExecutionPhase.BEFORE_TEST_METHOD),
+          @Sql(scripts = "single-book-reset.sql", executionPhase = ExecutionPhase.AFTER_TEST_METHOD)})
+  void findBookByTitle() {
+    Optional<Book> optionalBook = bookPersistenceAdapter.findBookByTitle("Get Your Hands Dirty on Clean Architecture");
+    assertThat(optionalBook).isPresent();
+  }
+
+  @Test
+  @SqlGroup({
+          @Sql(scripts = "single-book.sql", executionPhase = ExecutionPhase.BEFORE_TEST_METHOD),
+          @Sql(scripts = "single-book-reset.sql", executionPhase = ExecutionPhase.AFTER_TEST_METHOD)})
+  void savesBook() {
+    Book book = new Book(null, "A Hitchhiker's Guide to the Galaxy", 42L);
+    Book savedBook = bookPersistenceAdapter.saveBook(book);
+    assertThat(bookRepository.findById(savedBook.getId())).isPresent();
+  }
+
+}

src/test/java/io/reflectoring/reviewapp/application/port/in/RegisterBookCommandTests.java

@@ -0,0 +1,32 @@
+package io.reflectoring.reviewapp.application.port.in;
+
+import io.reflectoring.reviewapp.application.port.in.RegisterBookUseCase.RegisterBookCommand;
+import org.junit.jupiter.api.Test;
+
+import javax.validation.ConstraintViolationException;
+
+import static org.assertj.core.api.AssertionsForClassTypes.*;
+
+class RegisterBookCommandTests {
+
+  @Test
+  void acceptsValidParameters() {
+    new RegisterBookCommand("Get Your Hands Dirty on Clean Architecture", 42L);
+    // no exception
+  }
+
+  @Test
+  void rejectsEmptyTitle() {
+    assertThatThrownBy(() -> new RegisterBookCommand("", 42L))
+            .isInstanceOf(ConstraintViolationException.class);
+    assertThatThrownBy(() -> new RegisterBookCommand(null, 42L))
+            .isInstanceOf(ConstraintViolationException.class);
+  }
+
+  @Test
+  void rejectsEmptyAuthor() {
+    assertThatThrownBy(() -> new RegisterBookCommand("Get Your Hands Dirty on Clean Architecture", null))
+            .isInstanceOf(ConstraintViolationException.class);
+  }
+
+}