diff --git a/src/test/java/com/slotline/SlotlineApplicationTests.java b/src/test/java/com/slotline/SlotlineApplicationTests.java
new file mode 100644
index 0000000..58af295
--- /dev/null
+++ b/src/test/java/com/slotline/SlotlineApplicationTests.java
@@ -0,0 +1,12 @@
+package com.slotline;
+
+import org.junit.jupiter.api.Test;
+import org.springframework.boot.test.context.SpringBootTest;
+
+@SpringBootTest
+class SlotlineApplicationTests {
+
+    @Test
+    void contextLoads() {
+    }
+}
diff --git a/src/test/java/com/slotline/recurrence/RecurrenceExpanderTest.java b/src/test/java/com/slotline/recurrence/RecurrenceExpanderTest.java
new file mode 100644
index 0000000..ed54159
--- /dev/null
+++ b/src/test/java/com/slotline/recurrence/RecurrenceExpanderTest.java
@@ -0,0 +1,66 @@
+package com.slotline.recurrence;
+
+import org.junit.jupiter.api.Test;
+
+import java.time.Instant;
+import java.time.ZoneOffset;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class RecurrenceExpanderTest {
+
+    private final RecurrenceExpander expander = new RecurrenceExpander();
+
+    @Test
+    void expandsDailyWithIntervalAndCount() {
+        Instant start = Instant.parse("2026-09-01T10:00:00Z");
+        Instant end = Instant.parse("2026-09-01T11:00:00Z");
+
+        List<Occurrence> occurrences = expander.expand(start, end, "FREQ=DAILY;INTERVAL=2;COUNT=3", ZoneOffset.UTC);
+
+        assertThat(occurrences).extracting(Occurrence::start).containsExactly(
+                Instant.parse("2026-09-01T10:00:00Z"),
+                Instant.parse("2026-09-03T10:00:00Z"),
+                Instant.parse("2026-09-05T10:00:00Z"));
+        assertThat(occurrences).allSatisfy(occurrence ->
+                assertThat(occurrence.end()).isEqualTo(occurrence.start().plusSeconds(3600)));
+    }
+
+    @Test
+    void expandsWeeklyByDayInChronologicalOrder() {
+        Instant start = Instant.parse("2026-09-07T10:00:00Z");
+        Instant end = Instant.parse("2026-09-07T11:00:00Z");
+
+        List<Occurrence> occurrences = expander.expand(start, end, "FREQ=WEEKLY;BYDAY=MO,WE;COUNT=4", ZoneOffset.UTC);
+
+        assertThat(occurrences).extracting(Occurrence::start).containsExactly(
+                Instant.parse("2026-09-07T10:00:00Z"),
+                Instant.parse("2026-09-09T10:00:00Z"),
+                Instant.parse("2026-09-14T10:00:00Z"),
+                Instant.parse("2026-09-16T10:00:00Z"));
+    }
+
+    @Test
+    void stopsAtUntilBoundary() {
+        Instant start = Instant.parse("2026-09-01T10:00:00Z");
+        Instant end = Instant.parse("2026-09-01T11:00:00Z");
+
+        List<Occurrence> occurrences = expander.expand(start, end, "FREQ=DAILY;UNTIL=20260903T100000Z", ZoneOffset.UTC);
+
+        assertThat(occurrences).extracting(Occurrence::start).containsExactly(
+                Instant.parse("2026-09-01T10:00:00Z"),
+                Instant.parse("2026-09-02T10:00:00Z"),
+                Instant.parse("2026-09-03T10:00:00Z"));
+    }
+
+    @Test
+    void rejectsUnboundedRule() {
+        Instant start = Instant.parse("2026-09-01T10:00:00Z");
+        Instant end = Instant.parse("2026-09-01T11:00:00Z");
+
+        assertThatThrownBy(() -> expander.expand(start, end, "FREQ=DAILY", ZoneOffset.UTC))
+                .isInstanceOf(RecurrenceException.class);
+    }
+}
diff --git a/src/test/java/com/slotline/security/JwtServiceTest.java b/src/test/java/com/slotline/security/JwtServiceTest.java
new file mode 100644
index 0000000..c6f3d43
--- /dev/null
+++ b/src/test/java/com/slotline/security/JwtServiceTest.java
@@ -0,0 +1,45 @@
+package com.slotline.security;
+
+import com.slotline.config.SlotlineProperties;
+import com.slotline.user.Role;
+import io.jsonwebtoken.JwtException;
+import org.junit.jupiter.api.Test;
+
+import java.time.Duration;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+class JwtServiceTest {
+
+    private static JwtService serviceWithSecret(String secret) {
+        SlotlineProperties properties = new SlotlineProperties();
+        properties.getJwt().setSecret(secret);
+        properties.getJwt().setIssuer("slotline");
+        properties.getJwt().setExpiration(Duration.ofHours(1));
+        return new JwtService(properties);
+    }
+
+    @Test
+    void issuesAndParsesRoundTrip() {
+        JwtService jwtService = serviceWithSecret("round-trip-secret-round-trip-secret-0123456789");
+
+        String token = jwtService.issue(42L, "alice", Role.USER, 7L);
+        AuthenticatedUser parsed = jwtService.parse(token);
+
+        assertThat(parsed.id()).isEqualTo(42L);
+        assertThat(parsed.username()).isEqualTo("alice");
+        assertThat(parsed.role()).isEqualTo(Role.USER);
+        assertThat(parsed.organizationId()).isEqualTo(7L);
+    }
+
+    @Test
+    void rejectsTokenSignedWithAnotherSecret() {
+        JwtService issuer = serviceWithSecret("issuer-secret-issuer-secret-issuer-0123456789");
+        JwtService verifier = serviceWithSecret("verifier-secret-verifier-secret-diff-0123456789");
+
+        String token = issuer.issue(1L, "bob", Role.ADMIN, 3L);
+
+        assertThatThrownBy(() -> verifier.parse(token)).isInstanceOf(JwtException.class);
+    }
+}
diff --git a/src/test/resources/application-test.yml b/src/test/resources/application-test.yml
new file mode 100644
index 0000000..b3058df
--- /dev/null
+++ b/src/test/resources/application-test.yml
@@ -0,0 +1,5 @@
+spring:
+  datasource:
+    url: jdbc:h2:mem:slotline_concurrency;DB_CLOSE_DELAY=-1;LOCK_TIMEOUT=10000
+    hikari:
+      maximum-pool-size: 20