diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
new file mode 100644
index 0000000..4dafb39
--- /dev/null
+++ b/.github/workflows/ci.yml
@@ -0,0 +1,65 @@
+name: CI
+
+on:
+  push:
+    branches: [ master ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build-and-test:
+    name: Build, test and report coverage
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out repository
+        uses: actions/checkout@v4
+
+      - name: Set up JDK 8
+        uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: '8'
+
+      - name: Cache Gradle packages
+        uses: actions/cache@v4
+        with:
+          path: |
+            ~/.gradle/caches
+            ~/.gradle/wrapper
+          key: ${{ runner.os }}-gradle-${{ hashFiles('**/*.gradle', 'gradle/wrapper/gradle-wrapper.properties') }}
+          restore-keys: ${{ runner.os }}-gradle-
+
+      - name: Make Gradle wrapper executable
+        run: chmod +x ./gradlew
+
+      - name: Run tests with coverage
+        run: ./gradlew clean test jacocoTestReport jacocoTestCoverageVerification --no-daemon --stacktrace
+
+      - name: Coverage summary
+        if: always()
+        run: |
+          REPORT=build/reports/jacoco/test/jacocoTestReport.csv
+          if [ -f "$REPORT" ]; then
+            awk -F, 'NR>1 { lm += $8; lc += $9 } END {
+              total = lm + lc;
+              pct = (total > 0) ? lc * 100 / total : 0;
+              printf "## JaCoCo coverage\n\n| Metric | Value |\n|---|---|\n| Lines covered | %d / %d |\n| Line coverage | %.2f%% |\n", lc, total, pct
+            }' "$REPORT" >> "$GITHUB_STEP_SUMMARY"
+          else
+            echo "No JaCoCo report found." >> "$GITHUB_STEP_SUMMARY"
+          fi
+
+      - name: Upload test results
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: test-results
+          path: build/reports/tests/test
+
+      - name: Upload coverage report
+        if: always()
+        uses: actions/upload-artifact@v4
+        with:
+          name: jacoco-coverage-report
+          path: build/reports/jacoco/test
diff --git a/.gitignore b/.gitignore
index 57f1cb2..14e5aca 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,3 @@
-/.idea/
\ No newline at end of file
+/.idea/
+/.gradle/
+/build/
diff --git a/build.gradle b/build.gradle
index 09f1083..6788a23 100644
--- a/build.gradle
+++ b/build.gradle
@@ -10,6 +10,7 @@ buildscript {
 apply plugin: 'java'
 apply plugin: 'eclipse'
 apply plugin: 'idea'
+apply plugin: 'jacoco'
 apply plugin: 'org.springframework.boot'
 apply plugin: 'io.spring.dependency-management'
 
@@ -25,8 +26,52 @@ repositories {
 sourceCompatibility = 1.8
 targetCompatibility = 1.8
 
+ext {
+    junitVersion = '5.2.0'
+}
+
 dependencies {
     compile("org.springframework.boot:spring-boot-starter-web")
-    testCompile("junit:junit")
+    compile("org.springframework.boot:spring-boot-starter-jdbc")
+    compile("com.h2database:h2")
+    runtime("org.springframework.boot:spring-boot-properties-migrator")
+
+    testImplementation("org.junit.jupiter:junit-jupiter-api:${junitVersion}")
+    testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:${junitVersion}")
+}
+
+test {
+    useJUnitPlatform()
+    testLogging {
+        events "passed", "skipped", "failed"
+    }
+    finalizedBy jacocoTestReport
+}
+
+jacoco {
+    toolVersion = "0.8.5"
+}
+
+jacocoTestReport {
+    dependsOn test
+    reports {
+        xml.enabled true
+        html.enabled true
+        csv.enabled true
+    }
+}
+
+jacocoTestCoverageVerification {
+    violationRules {
+        rule {
+            element = 'BUNDLE'
+            limit {
+                counter = 'LINE'
+                value = 'COVEREDRATIO'
+                minimum = 0.60
+            }
+        }
+    }
 }
 
+check.dependsOn jacocoTestCoverageVerification
diff --git a/gradlew b/gradlew
old mode 100644
new mode 100755
diff --git a/src/test/java/hello/controller/GreetingControllerTest.java b/src/test/java/hello/controller/GreetingControllerTest.java
new file mode 100644
index 0000000..bf7ccc4
--- /dev/null
+++ b/src/test/java/hello/controller/GreetingControllerTest.java
@@ -0,0 +1,28 @@
+package hello.controller;
+
+import hello.model.Greeting;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class GreetingControllerTest {
+
+    @Test
+    void greetingUsesDefaultNameAndIncrementsCounter() {
+        GreetingController controller = new GreetingController();
+
+        Greeting first = controller.greeting("World");
+        assertEquals(1L, first.getId());
+        assertEquals("Hello, World!", first.getContent());
+
+        Greeting second = controller.greeting("World");
+        assertEquals(2L, second.getId());
+    }
+
+    @Test
+    void greetingUsesProvidedName() {
+        GreetingController controller = new GreetingController();
+        Greeting greeting = controller.greeting("Matthew");
+        assertEquals("Hello, Matthew!", greeting.getContent());
+    }
+}
diff --git a/src/test/java/hello/controller/HelloControllerTest.java b/src/test/java/hello/controller/HelloControllerTest.java
new file mode 100644
index 0000000..f6ff611
--- /dev/null
+++ b/src/test/java/hello/controller/HelloControllerTest.java
@@ -0,0 +1,48 @@
+package hello.controller;
+
+import hello.service.TopicService;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class HelloControllerTest {
+
+    private HelloController controller;
+
+    @BeforeEach
+    void setUp() throws Exception {
+        controller = new HelloController();
+        Field field = HelloController.class.getDeclaredField("topicService");
+        field.setAccessible(true);
+        field.set(controller, new TopicService());
+    }
+
+    @Test
+    void indexReturnsDateTimeGreeting() {
+        String result = controller.index();
+        assertNotNull(result);
+        assertTrue(result.startsWith("Greetings from Spring Boot!"));
+        assertTrue(result.contains("Is this a leap year ?"));
+    }
+
+    @Test
+    void showStringOperationCombinesServiceResults() {
+        String result = controller.showStringOperation();
+        assertTrue(result.contains("spring:java:javascript"));
+        assertTrue(result.contains("java:javascript"));
+        assertTrue(result.contains("[spring]"));
+    }
+
+    @Test
+    void showFileOperationReturnsCombinedFileResults() {
+        String result = controller.showFileOperation();
+        assertNotNull(result);
+        assertFalse(result.contains("IO exception"));
+        assertTrue(result.contains("Find all files in path and sort"));
+    }
+}
diff --git a/src/test/java/hello/controller/TopicControllerTest.java b/src/test/java/hello/controller/TopicControllerTest.java
new file mode 100644
index 0000000..0fa24c9
--- /dev/null
+++ b/src/test/java/hello/controller/TopicControllerTest.java
@@ -0,0 +1,69 @@
+package hello.controller;
+
+import hello.model.Topic;
+import hello.service.TopicService;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import java.lang.reflect.Field;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+
+class TopicControllerTest {
+
+    private TopicController controller;
+
+    @BeforeEach
+    void setUp() throws Exception {
+        controller = new TopicController();
+        Field field = TopicController.class.getDeclaredField("topicService");
+        field.setAccessible(true);
+        field.set(controller, new TopicService());
+    }
+
+    private List<String> ids(List<Topic> topics) {
+        return topics.stream().map(Topic::getId).collect(Collectors.toList());
+    }
+
+    @Test
+    void getAllTopicsDelegatesToService() {
+        assertEquals(Arrays.asList("spring", "java", "javascript"), ids(controller.getAllTopics()));
+    }
+
+    @Test
+    void getTopicWithIdDelegatesToService() {
+        assertEquals("Core Java", controller.getTopicWithID("java").getSubjectName());
+    }
+
+    @Test
+    void addTopicDelegatesToService() {
+        controller.addTopic(new Topic("go", "Go Lang", "Go Description"));
+        assertEquals(4, controller.getAllTopics().size());
+    }
+
+    @Test
+    void updateTopicDelegatesToService() {
+        controller.updateTopic("java", new Topic("java", "Modern Java", "Updated"));
+        assertEquals("Modern Java", controller.getTopicWithID("java").getSubjectName());
+    }
+
+    @Test
+    void deleteTopicDelegatesToService() {
+        controller.deleteTopic("java");
+        assertFalse(ids(controller.getAllTopics()).contains("java"));
+    }
+
+    @Test
+    void filterMinimumLengthForIdDelegatesToService() {
+        assertEquals(Arrays.asList("javascript"), ids(controller.filterMinimumLengthForId(6)));
+    }
+
+    @Test
+    void sortTopicsWithIdDelegatesToService() {
+        assertEquals(Arrays.asList("java", "javascript", "spring"), ids(controller.sortTopicsWithID()));
+    }
+}
diff --git a/src/test/java/hello/declaration/TimeClientTest.java b/src/test/java/hello/declaration/TimeClientTest.java
new file mode 100644
index 0000000..b633da5
--- /dev/null
+++ b/src/test/java/hello/declaration/TimeClientTest.java
@@ -0,0 +1,33 @@
+package hello.declaration;
+
+import hello.model.SimpleTimeClient;
+import org.junit.jupiter.api.Test;
+
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class TimeClientTest {
+
+    @Test
+    void getZoneIdReturnsRequestedZoneWhenValid() {
+        assertEquals(ZoneId.of("Europe/London"), TimeClient.getZoneId("Europe/London"));
+    }
+
+    @Test
+    void getZoneIdFallsBackToSystemDefaultWhenInvalid() {
+        assertEquals(ZoneId.systemDefault(), TimeClient.getZoneId("Not/AZone"));
+    }
+
+    @Test
+    void getZonedDateTimeUsesLocalDateTimeAndZone() {
+        SimpleTimeClient client = new SimpleTimeClient();
+        client.setDateAndTime(2021, 6, 20, 10, 30, 45);
+
+        ZonedDateTime zoned = client.getZonedDateTime("America/New_York");
+
+        assertEquals(client.getLocalDateTime(), zoned.toLocalDateTime());
+        assertEquals(ZoneId.of("America/New_York"), zoned.getZone());
+    }
+}
diff --git a/src/test/java/hello/model/ModelPojoTest.java b/src/test/java/hello/model/ModelPojoTest.java
new file mode 100644
index 0000000..fd9fd71
--- /dev/null
+++ b/src/test/java/hello/model/ModelPojoTest.java
@@ -0,0 +1,81 @@
+package hello.model;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ModelPojoTest {
+
+    @Test
+    void topicAllArgsConstructorAndGetters() {
+        Topic topic = new Topic("java", "Core Java", "Java Description");
+        assertEquals("java", topic.getId());
+        assertEquals("Core Java", topic.getSubjectName());
+        assertEquals("Java Description", topic.getSubjectDescription());
+    }
+
+    @Test
+    void topicNoArgsConstructorAndSetters() {
+        Topic topic = new Topic();
+        topic.setId("go");
+        topic.setSubjectName("Go Lang");
+        topic.setSubjectDescription("Go Description");
+        assertEquals("go", topic.getId());
+        assertEquals("Go Lang", topic.getSubjectName());
+        assertEquals("Go Description", topic.getSubjectDescription());
+    }
+
+    @Test
+    void greetingIsImmutable() {
+        Greeting greeting = new Greeting(42L, "Hello, World!");
+        assertEquals(42L, greeting.getId());
+        assertEquals("Hello, World!", greeting.getContent());
+    }
+
+    @Test
+    void customerGettersSettersAndToString() {
+        Customer customer = new Customer(1L, "Josh", "Bloch");
+        assertEquals(1L, customer.getId());
+        assertEquals("Josh", customer.getFirstName());
+        assertEquals("Bloch", customer.getLastName());
+
+        customer.setId(2L);
+        customer.setFirstName("Jeff");
+        customer.setLastName("Dean");
+        assertEquals(2L, customer.getId());
+        assertEquals("Jeff", customer.getFirstName());
+        assertEquals("Dean", customer.getLastName());
+
+        String text = customer.toString();
+        assertTrue(text.contains("Jeff"));
+        assertTrue(text.contains("Dean"));
+        assertTrue(text.contains("id=2"));
+    }
+
+    @Test
+    void valueGettersSettersAndToString() {
+        Value value = new Value();
+        value.setId(7L);
+        value.setQuote("Stay hungry");
+        assertEquals(Long.valueOf(7L), value.getId());
+        assertEquals("Stay hungry", value.getQuote());
+        assertTrue(value.toString().contains("Stay hungry"));
+    }
+
+    @Test
+    void quoteGettersSettersAndToString() {
+        Value value = new Value();
+        value.setId(1L);
+        value.setQuote("Work hard");
+
+        Quote quote = new Quote();
+        quote.setType("success");
+        quote.setValue(value);
+
+        assertEquals("success", quote.getType());
+        assertEquals(value, quote.getValue());
+        assertTrue(quote.toString().contains("success"));
+        assertTrue(quote.toString().contains("Work hard"));
+    }
+}
diff --git a/src/test/java/hello/model/SimpleTimeClientTest.java b/src/test/java/hello/model/SimpleTimeClientTest.java
new file mode 100644
index 0000000..74f8769
--- /dev/null
+++ b/src/test/java/hello/model/SimpleTimeClientTest.java
@@ -0,0 +1,40 @@
+package hello.model;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.LocalDateTime;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+class SimpleTimeClientTest {
+
+    @Test
+    void setDateAndTimeSetsFullTimestamp() {
+        SimpleTimeClient client = new SimpleTimeClient();
+        client.setDateAndTime(2021, 6, 20, 10, 30, 45);
+        assertEquals(LocalDateTime.of(2021, 6, 20, 10, 30, 45), client.getLocalDateTime());
+    }
+
+    @Test
+    void toStringMatchesLocalDateTime() {
+        SimpleTimeClient client = new SimpleTimeClient();
+        client.setDateAndTime(2021, 6, 20, 10, 30, 45);
+        assertEquals(client.getLocalDateTime().toString(), client.toString());
+    }
+
+    @Test
+    void setTimeKeepsDateAndUpdatesTime() {
+        SimpleTimeClient client = new SimpleTimeClient();
+        client.setDateAndTime(2021, 6, 20, 10, 30, 45);
+        client.setTime(1, 2, 3);
+        assertEquals(LocalDateTime.of(2021, 6, 20, 1, 2, 3), client.getLocalDateTime());
+    }
+
+    @Test
+    void setDateKeepsTimeAndUpdatesDate() {
+        SimpleTimeClient client = new SimpleTimeClient();
+        client.setDateAndTime(2021, 6, 20, 10, 30, 45);
+        client.setDate(2000, 1, 1);
+        assertEquals(LocalDateTime.of(2000, 1, 1, 10, 30, 45), client.getLocalDateTime());
+    }
+}
diff --git a/src/test/java/hello/service/TopicServiceTest.java b/src/test/java/hello/service/TopicServiceTest.java
new file mode 100644
index 0000000..36d11bd
--- /dev/null
+++ b/src/test/java/hello/service/TopicServiceTest.java
@@ -0,0 +1,182 @@
+package hello.service;
+
+import hello.model.Topic;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.NoSuchElementException;
+import java.util.stream.Collectors;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class TopicServiceTest {
+
+    private TopicService service;
+
+    @BeforeEach
+    void setUp() {
+        service = new TopicService();
+    }
+
+    private List<String> ids(List<Topic> topics) {
+        return topics.stream().map(Topic::getId).collect(Collectors.toList());
+    }
+
+    @Nested
+    @DisplayName("CRUD list operations")
+    class CrudOperations {
+
+        @Test
+        void getAllTopicsReturnsSeededTopics() {
+            List<Topic> all = service.getAllTopics();
+            assertEquals(3, all.size());
+            assertEquals(Arrays.asList("spring", "java", "javascript"), ids(all));
+        }
+
+        @Test
+        void getTopicWithIdReturnsMatchingTopic() {
+            Topic topic = service.getTopicWithId("java");
+            assertEquals("java", topic.getId());
+            assertEquals("Core Java", topic.getSubjectName());
+        }
+
+        @Test
+        void getTopicWithIdThrowsWhenMissing() {
+            assertThrows(NoSuchElementException.class, () -> service.getTopicWithId("missing"));
+        }
+
+        @Test
+        void addTopicAppendsToList() {
+            service.addTopic(new Topic("go", "Go Lang", "Go Description"));
+            assertEquals(4, service.getAllTopics().size());
+            assertEquals("go", service.getTopicWithId("go").getId());
+        }
+
+        @Test
+        void updateTopicReplacesExistingEntry() {
+            service.updateTopic("java", new Topic("java", "Modern Java", "Updated"));
+            assertEquals("Modern Java", service.getTopicWithId("java").getSubjectName());
+            assertEquals(3, service.getAllTopics().size());
+        }
+
+        @Test
+        void updateTopicIsNoOpWhenIdNotFound() {
+            service.updateTopic("missing", new Topic("missing", "Nope", "Nope"));
+            assertEquals(3, service.getAllTopics().size());
+            assertEquals(Arrays.asList("spring", "java", "javascript"), ids(service.getAllTopics()));
+        }
+
+        @Test
+        void deleteTopicRemovesMatchingEntry() {
+            service.deleteTopic("java");
+            assertEquals(2, service.getAllTopics().size());
+            assertFalse(ids(service.getAllTopics()).contains("java"));
+        }
+    }
+
+    @Nested
+    @DisplayName("Filtering and sorting")
+    class FilteringAndSorting {
+
+        @Test
+        void filterMinimumLengthForIdKeepsLongerIds() {
+            List<Topic> filtered = service.filterMinimumLengthForId(6);
+            assertEquals(Arrays.asList("javascript"), ids(filtered));
+        }
+
+        @Test
+        void filterMinimumLengthForIdReturnsEmptyWhenNoneQualify() {
+            assertTrue(service.filterMinimumLengthForId(100).isEmpty());
+        }
+
+        @Test
+        void sortTopicsWithIdSortsAlphabetically() {
+            List<Topic> sorted = service.sortTopicsWithID();
+            assertEquals(Arrays.asList("java", "javascript", "spring"), ids(sorted));
+        }
+    }
+
+    @Nested
+    @DisplayName("String / stream transforms")
+    class StringOperations {
+
+        @Test
+        void returnAllTopicIdWithStringSlicingJoinsWithColon() {
+            assertEquals("spring:java:javascript", service.returnAllTopicIDWithStringSlicing());
+        }
+
+        @Test
+        void makeDistinctAndSortCharactersRemovesDuplicatesAndSorts() {
+            assertEquals("abcr", service.makeDistinctAndSortCharacters("cabbra"));
+        }
+
+        @Test
+        void makeDistinctAndSortCharactersHandlesColonsAndLetters() {
+            assertEquals(":acgijnprstv", service.makeDistinctAndSortCharacters("spring:java:javascript"));
+        }
+
+        @Test
+        void makeDistinctAndSortCharactersEmptyInput() {
+            assertEquals("", service.makeDistinctAndSortCharacters(""));
+        }
+
+        @Test
+        void splitAllIdSelectsOnlyEntriesContainingJavaSortedAndJoined() {
+            String result = service.splitAllIdWithColonSelectIDWithJavaKeywordThenSortThenJoin(
+                    "spring:java:javascript");
+            assertEquals("java:javascript", result);
+        }
+
+        @Test
+        void splitAllIdReturnsEmptyWhenNoJavaKeyword() {
+            assertEquals("", service.splitAllIdWithColonSelectIDWithJavaKeywordThenSortThenJoin("spring:go:rust"));
+        }
+
+        @Test
+        void findIdHavingCharacterReturnsIdsContainingLetterG() {
+            assertEquals("[spring]", service.findIdHavingCharacter());
+        }
+    }
+
+    @Nested
+    @DisplayName("File / NIO operations")
+    class FileOperations {
+
+        @Test
+        void findAllFilesInPathAndSortListsProjectFiles() {
+            String result = service.findAllFilesInPathAndSort();
+            assertNotNull(result);
+            assertFalse(result.startsWith(" Error"));
+            assertTrue(result.contains("src"), "expected listing to contain project sources: " + result);
+        }
+
+        @Test
+        void findParticularFileInPathAndSortFindsGradleFiles() {
+            String result = service.findParticularFileInPathAndSort();
+            assertNotNull(result);
+            assertFalse(result.contains("IO exception"));
+            assertTrue(result.contains("grad"), "expected to find gradle files: " + result);
+        }
+
+        @Test
+        void findParticularFileInPathAndSortWithWalkFunctionFindsGradleFiles() {
+            String result = service.findParticularFileInPathAndSortWithWalkFunction();
+            assertNotNull(result);
+            assertFalse(result.contains("IO exception"));
+            assertTrue(result.contains("grad"), "expected to find gradle files: " + result);
+        }
+
+        @Test
+        void readFileWithStreamFunctionExtractsPrintLines() {
+            assertEquals(" Hello, this, is, Rehman", service.readFileWithStreamFunction());
+        }
+    }
+}