diff --git a/space-client/src/main/java/io/github/pgmarc/space/contracts/AddOn.java b/space-client/src/main/java/io/github/pgmarc/space/contracts/AddOn.java
index 0e54a89..3bebbc6 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/contracts/AddOn.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/contracts/AddOn.java
@@ -31,4 +31,12 @@ public boolean equals(Object o) {
     public int hashCode() {
         return Objects.hash(name, quantity);
     }
+
+    @Override
+    public String toString() {
+        return "AddOn{" +
+            "name='" + name + '\'' +
+            ", quantity=" + quantity +
+            '}';
+    }
 }
diff --git a/space-client/src/main/java/io/github/pgmarc/space/contracts/Service.java b/space-client/src/main/java/io/github/pgmarc/space/contracts/Service.java
index 67697c3..04bd601 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/contracts/Service.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/contracts/Service.java
@@ -46,11 +46,6 @@ public static Builder builder(String name, String version) {
         return new Builder(name, version);
     }
 
-    @Override
-    public String toString() {
-        return name + ": " + version + " plan" + plan + " addOns " + addOns;
-    }
-
     @Override
     public boolean equals(Object o) {
         if (o == null || getClass() != o.getClass()) return false;
@@ -63,6 +58,16 @@ public int hashCode() {
         return Objects.hash(name, version, addOns, plan);
     }
 
+    @Override
+    public String toString() {
+        return "Service{" +
+            "name='" + name + '\'' +
+            ", version='" + version + '\'' +
+            ", addOns=" + addOns +
+            ", plan='" + plan + '\'' +
+            '}';
+    }
+
     public static final class Builder {
 
         private final String name;
diff --git a/space-client/src/main/java/io/github/pgmarc/space/contracts/Subscription.java b/space-client/src/main/java/io/github/pgmarc/space/contracts/Subscription.java
index 2796ac8..8dc2c34 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/contracts/Subscription.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/contracts/Subscription.java
@@ -1,15 +1,10 @@
 package io.github.pgmarc.space.contracts;
 
-import java.time.*;
-import java.util.ArrayList;
-import java.util.Collection;
-import java.util.Collections;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
-import java.util.Objects;
-import java.util.Optional;
-import java.util.Set;
+import java.time.LocalDateTime;
+import java.time.Period;
+import java.time.ZoneId;
+import java.time.ZonedDateTime;
+import java.util.*;
 import java.util.stream.Collectors;
 
 public final class Subscription {
@@ -24,12 +19,12 @@ public final class Subscription {
 
     private Subscription(Builder builder) {
         this.userContact = builder.userContact;
+        this.services = builder.services;
         this.startDate = builder.startDate;
         this.endDate = builder.endDate;
         this.renewalPeriod = builder.renewalPeriod;
-        this.services = Collections.unmodifiableMap(builder.services);
-        this.history = Collections.unmodifiableList(builder.history);
-        this.usageLevels = Collections.unmodifiableMap(builder.usageLevels);
+        this.history = builder.history;
+        this.usageLevels = builder.usageLevels;
     }
 
     public static Builder builder(UserContact userContact, ZonedDateTime startDate, ZonedDateTime endDate,
@@ -41,6 +36,14 @@ public static Builder builder(UserContact userContact, ZonedDateTime startDate,
         return new Builder(userContact, startDate, endDate).subscribeAll(services);
     }
 
+    public String getUserId() {
+        return userContact.getUserId();
+    }
+
+    public String getUsername() {
+        return userContact.getUsername();
+    }
+
     public LocalDateTime getStartDate() {
         return startDate.toLocalDateTime();
     }
@@ -58,7 +61,8 @@ public boolean isAutoRenewable() {
     }
 
     public Optional<LocalDateTime> getRenewalDate() {
-        return Optional.ofNullable(isAutoRenewable() ? endDate.plus(renewalPeriod).toLocalDateTime() : null);
+        return Optional.ofNullable(renewalPeriod)
+            .map( renewalPeriod -> endDate.plus(renewalPeriod).toLocalDateTime());
     }
 
     /**
@@ -84,33 +88,52 @@ public boolean isExpired(LocalDateTime date) {
         return startDate.isBefore(utcDate) && endDate.isBefore(utcDate);
     }
 
-
-    public String getUserId() {
-        return userContact.getUserId();
+    public Map<String, Service> getServicesMap() {
+        return Collections.unmodifiableMap(services);
     }
 
-    public String getUsername() {
-        return userContact.getUsername();
+    public Collection<Service> getServices() {
+        return Collections.unmodifiableCollection(services.values());
     }
 
     public Optional<Service> getService(String serviceName) {
         return Optional.ofNullable(this.services.get(serviceName));
     }
 
-    public Map<String, Service> getServicesMap() {
-        return services;
+    public List<Snapshot> getHistory() {
+        return Collections.unmodifiableList(history);
     }
 
-    public Set<Service> getServices() {
-        return Set.copyOf(services.values());
+    public Map<String, Map<String, UsageLevel>> getUsageLevels() {
+        return Collections.unmodifiableMap(usageLevels);
     }
 
-    public List<Snapshot> getHistory() {
-        return history;
+    public Optional<Map<String, UsageLevel>> getServiceUsageLevels(String service) {
+        Objects.requireNonNull(service, "service name must not be null");
+        return Optional.ofNullable(usageLevels.get(service));
     }
 
-    public Map<String, Map<String, UsageLevel>> getUsageLevels() {
-        return usageLevels;
+    public Optional<UsageLevel> getUsageLevel(String service, String usageLimit) {
+        Objects.requireNonNull(service, "service name must not be null");
+        Objects.requireNonNull(usageLimit, "usage limit name must not be null");
+        if (!usageLevels.containsKey(service)) {
+            return Optional.empty();
+        }
+        return Optional.ofNullable(usageLevels.get(service).get(usageLimit));
+
+    }
+
+    @Override
+    public String toString() {
+        return "Subscription{" +
+            "userContact=" + userContact +
+            ", services=" + services +
+            ", startDate=" + startDate +
+            ", endDate=" + endDate +
+            ", renewalPeriod=" + renewalPeriod +
+            ", history=" + history +
+            ", usageLevels=" + usageLevels +
+            '}';
     }
 
     public enum Keys {
@@ -256,5 +279,26 @@ public static Snapshot of(ZonedDateTime startDateTime, ZonedDateTime endDateTime
                                   Map<String, Service> services) {
             return new Snapshot(startDateTime, endDateTime, services);
         }
+
+        @Override
+        public boolean equals(Object o) {
+            if (o == null || getClass() != o.getClass()) return false;
+            Snapshot snapshot = (Snapshot) o;
+            return Objects.equals(starDateTime, snapshot.starDateTime) && Objects.equals(endDateTime, snapshot.endDateTime) && Objects.equals(services, snapshot.services);
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(starDateTime, endDateTime, services);
+        }
+
+        @Override
+        public String toString() {
+            return "Snapshot{" +
+                "starDateTime=" + starDateTime +
+                ", endDateTime=" + endDateTime +
+                ", services=" + services +
+                '}';
+        }
     }
 }
diff --git a/space-client/src/main/java/io/github/pgmarc/space/contracts/SubscriptionRequest.java b/space-client/src/main/java/io/github/pgmarc/space/contracts/SubscriptionRequest.java
index b4ad24a..2bf56e1 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/contracts/SubscriptionRequest.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/contracts/SubscriptionRequest.java
@@ -1,6 +1,6 @@
 package io.github.pgmarc.space.contracts;
 
-import java.time.Duration;
+import java.time.Period;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
@@ -11,12 +11,12 @@ public final class SubscriptionRequest {
 
     private final UserContact userContact;
     private final Set<Service> services;
-    private final Duration renewalDays;
+    private final Period renewalPeriod;
 
     private SubscriptionRequest(Builder builder) {
         this.userContact = builder.userContact;
-        this.renewalDays = builder.renewalDays;
-        this.services = Collections.unmodifiableSet(builder.services);
+        this.renewalPeriod = builder.renewalPeriod;
+        this.services = builder.services;
     }
 
     public static Builder builder(UserContact userContact) {
@@ -27,12 +27,12 @@ public UserContact getUserContact() {
         return userContact;
     }
 
-    public Set<Service> getServices() {
-        return services;
+    public Collection<Service> getServices() {
+        return Collections.unmodifiableCollection(services);
     }
 
-    public Duration getRenewalDays() {
-        return renewalDays;
+    public Period getRenewalPeriod() {
+        return renewalPeriod;
     }
 
     public static final class Builder {
@@ -40,7 +40,7 @@ public static final class Builder {
         private final UserContact userContact;
         private final Set<Service> services = new HashSet<>();
         private Service.Builder serviceBuilder;
-        private Duration renewalDays;
+        private Period renewalPeriod;
 
         private Builder(UserContact userContact) {
             this.userContact = userContact;
@@ -53,12 +53,18 @@ public Builder subscribe(Service service) {
 
         public Builder subscribeAll(Collection<Service> services) {
             Objects.requireNonNull(services, "services must not be null");
+            if (services.isEmpty()) {
+                throw  new IllegalArgumentException("services must not be empty");
+            }
             this.services.addAll(services);
             return this;
         }
 
-        public Builder renewIn(Duration renewalDays) {
-            this.renewalDays = renewalDays;
+        public Builder renewInDays(int days) {
+            if (days < 1) {
+                throw new IllegalArgumentException("renewal period given in days must be positive");
+            }
+            this.renewalPeriod = Period.ofDays(days);
             return this;
         }
 
diff --git a/space-client/src/main/java/io/github/pgmarc/space/contracts/UsageLevel.java b/space-client/src/main/java/io/github/pgmarc/space/contracts/UsageLevel.java
index b980b43..10b43de 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/contracts/UsageLevel.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/contracts/UsageLevel.java
@@ -38,7 +38,7 @@ public String getName() {
     }
 
     public Optional<LocalDateTime> getResetTimestamp() {
-        return resetTimestamp != null ? Optional.of(resetTimestamp.toLocalDateTime()) : Optional.empty();
+        return Optional.ofNullable(resetTimestamp).map(ZonedDateTime::toLocalDateTime);
     }
 
     public boolean isRenewableUsageLimit() {
@@ -51,8 +51,8 @@ public double getConsumption() {
 
     private static void validateUsageLevel(String name, double consumed) {
         Objects.requireNonNull(name, "usage limit name must not be null");
-        if (consumed <= 0) {
-            throw new IllegalArgumentException("consumption must be greater than 0");
+        if (consumed < 0) {
+            throw new IllegalArgumentException("usage level consumption must be positive");
         }
     }
 
@@ -76,4 +76,13 @@ public boolean equals(Object o) {
     public int hashCode() {
         return Objects.hash(name, consumed, resetTimestamp);
     }
+
+    @Override
+    public String toString() {
+        return "UsageLevel{" +
+            "name='" + name + '\'' +
+            ", consumed=" + consumed +
+            ", resetTimestamp=" + resetTimestamp +
+            '}';
+    }
 }
diff --git a/space-client/src/main/java/io/github/pgmarc/space/contracts/UserContact.java b/space-client/src/main/java/io/github/pgmarc/space/contracts/UserContact.java
index 95f17b3..a19a344 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/contracts/UserContact.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/contracts/UserContact.java
@@ -21,12 +21,6 @@ private UserContact(Builder builder) {
         this.phone = builder.phone;
     }
 
-    public static Builder builder(String userId, String username) {
-        Objects.requireNonNull(userId, "userId must not be null");
-        Objects.requireNonNull(username, "username must not be null");
-        return new Builder(userId, username);
-    }
-
     public String getUserId() {
         return userId;
     }
@@ -51,35 +45,34 @@ public Optional<String> getPhone() {
         return Optional.ofNullable(phone);
     }
 
+    @Override
+    public boolean equals(Object o) {
+        if (o == null || getClass() != o.getClass()) return false;
+        UserContact that = (UserContact) o;
+        return Objects.equals(userId, that.userId) && Objects.equals(username, that.username);
+    }
+
     @Override
     public int hashCode() {
-        final int prime = 31;
-        int result = 1;
-        result = prime * result + ((userId == null) ? 0 : userId.hashCode());
-        result = prime * result + ((username == null) ? 0 : username.hashCode());
-        return result;
+        return Objects.hash(userId, username);
     }
 
     @Override
-    public boolean equals(Object obj) {
-        if (this == obj)
-            return true;
-        if (obj == null)
-            return false;
-        if (getClass() != obj.getClass())
-            return false;
-        UserContact other = (UserContact) obj;
-        if (userId == null) {
-            if (other.userId != null)
-                return false;
-        } else if (!userId.equals(other.userId))
-            return false;
-        if (username == null) {
-            if (other.username != null)
-                return false;
-        } else if (!username.equals(other.username))
-            return false;
-        return true;
+    public String toString() {
+        return "UserContact{" +
+            "userId='" + userId + '\'' +
+            ", username='" + username + '\'' +
+            ", firstName='" + firstName + '\'' +
+            ", lastName='" + lastName + '\'' +
+            ", email='" + email + '\'' +
+            ", phone='" + phone + '\'' +
+            '}';
+    }
+
+    public static Builder builder(String userId, String username) {
+        Objects.requireNonNull(userId, "userId must not be null");
+        Objects.requireNonNull(username, "username must not be null");
+        return new Builder(userId, username);
     }
 
     public static class Builder {
@@ -145,7 +138,7 @@ public enum Keys {
 
         private final String name;
 
-        private Keys(String name) {
+        Keys(String name) {
             this.name = name;
         }
 
diff --git a/space-client/src/main/java/io/github/pgmarc/space/features/FeatureEvaluationResult.java b/space-client/src/main/java/io/github/pgmarc/space/features/FeatureEvaluationResult.java
index 9f95e27..13afac7 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/features/FeatureEvaluationResult.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/features/FeatureEvaluationResult.java
@@ -39,6 +39,14 @@ public static FeatureEvaluationResult of(boolean available, Map<String,Usage> qu
         return new FeatureEvaluationResult(available, quotas);
     }
 
+    @Override
+    public String toString() {
+        return "FeatureEvaluationResult{" +
+            "available=" + available +
+            ", quotas=" + quotas +
+            '}';
+    }
+
     public static final class Usage {
 
         private final Number used;
@@ -60,6 +68,14 @@ public Number getLimit() {
         public static Usage of(Number used, Number limit) {
             return new Usage(used, limit);
         }
+
+        @Override
+        public String toString() {
+            return "Usage{" +
+                "used=" + used +
+                ", limit=" + limit +
+                '}';
+        }
     }
 
 }
diff --git a/space-client/src/main/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializer.java b/space-client/src/main/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializer.java
index 1d71f71..8c957b8 100644
--- a/space-client/src/main/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializer.java
+++ b/space-client/src/main/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializer.java
@@ -1,5 +1,6 @@
 package io.github.pgmarc.space.serializers;
 
+import java.time.temporal.ChronoUnit;
 import java.util.*;
 
 import org.json.JSONObject;
@@ -18,14 +19,14 @@ public JSONObject toJson(SubscriptionRequest object) {
         JSONObject json = new JSONObject()
                 .put(Subscription.Keys.USER_CONTACT.toString(), userContact(object.getUserContact()))
                 .put(Subscription.Keys.BILLING_PERIOD.toString(),
-                        Map.of("autoRenew", object.getRenewalDays() != null))
+                        Map.of("autoRenew", object.getRenewalPeriod() != null))
                 .put(Subscription.Keys.CONTRACTED_SERVICES.toString(), contractedServices(object.getServices()))
                 .put(Subscription.Keys.SUBSCRIPTION_PLANS.toString(), subscriptionPlans(object.getServices()))
                 .put(Subscription.Keys.SUBSCRIPTION_ADDONS.toString(), subscriptionAddOns(object.getServices()));
 
-        if (object.getRenewalDays() != null) {
+        if (object.getRenewalPeriod() != null) {
             json.getJSONObject(Subscription.Keys.BILLING_PERIOD.toString())
-                    .put("renewalDays", object.getRenewalDays().toDays());
+                    .put("renewalDays", object.getRenewalPeriod().getDays());
         }
 
         return json;
@@ -42,7 +43,7 @@ public Map<String, String> userContact(UserContact userContact) {
         return res;
     }
 
-    public static Map<String, String> contractedServices(Set<Service> services) {
+    public static Map<String, String> contractedServices(Collection<Service> services) {
         Map<String, String> res = new HashMap<>();
         for (Service service : services) {
             res.put(service.getName(), service.getVersion());
@@ -50,7 +51,7 @@ public static Map<String, String> contractedServices(Set<Service> services) {
         return Collections.unmodifiableMap(res);
     }
 
-    public static Map<String, String> subscriptionPlans(Set<Service> services) {
+    public static Map<String, String> subscriptionPlans(Collection<Service> services) {
         Map<String, String> res = new HashMap<>();
         for (Service service : services) {
             Optional<String> plan = service.getPlan();
@@ -63,7 +64,7 @@ public static Map<String, String> subscriptionPlans(Set<Service> services) {
 
     }
 
-    public static Map<String, Map<String, Long>> subscriptionAddOns(Set<Service> services) {
+    public static Map<String, Map<String, Long>> subscriptionAddOns(Collection<Service> services) {
 
         Map<String, Map<String, Long>> res = new HashMap<>();
 
diff --git a/space-client/src/test/java/io/github/pgmarc/space/ContractsEndpointTest.java b/space-client/src/test/java/io/github/pgmarc/space/ContractsEndpointTest.java
index 5183632..004f17c 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/ContractsEndpointTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/ContractsEndpointTest.java
@@ -68,7 +68,7 @@ void givenASubscriptionShouldBeCreated() {
                 .build();
 
         SubscriptionRequest subReq = SubscriptionRequest.builder(userContact)
-                .renewIn(Duration.ofDays(45))
+                .renewInDays(renewalDays)
                 .startService("zoom", "2025")
                     .plan("ENTERPRISE")
                     .addOn("extraSeats", 2)
@@ -84,9 +84,9 @@ void givenASubscriptionShouldBeCreated() {
         Subscription subscription;
         try {
             subscription = endpoint.addContract(subReq);
-            assertThat(subscription.getServices()).isEqualTo(subReq.getServices());
+            assertThat(subscription.getServices()).containsAll(subReq.getServices());
             assertThat(subscription.getUserId()).isEqualTo(userId);
-            assertThat(subscription.getRenewalPeriod()).hasValue(Period.ofDays(45));
+            assertThat(subscription.getRenewalPeriod()).hasValue(Period.ofDays(renewalDays));
             assertThat(subscription.getHistory()).isEmpty();
         } catch (IOException e) {
             fail();
diff --git a/space-client/src/test/java/io/github/pgmarc/space/FeaturesEndpointTest.java b/space-client/src/test/java/io/github/pgmarc/space/FeaturesEndpointTest.java
index b2a50e8..0c93455 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/FeaturesEndpointTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/FeaturesEndpointTest.java
@@ -2,9 +2,9 @@
 
 import com.github.tomakehurst.wiremock.junit5.WireMockRuntimeInfo;
 import com.github.tomakehurst.wiremock.junit5.WireMockTest;
+import io.github.pgmarc.space.features.FeatureEvaluationResult;
 import io.github.pgmarc.space.features.Revert;
 import io.github.pgmarc.space.features.UsageLimitConsumption;
-import io.github.pgmarc.space.features.FeatureEvaluationResult;
 import okhttp3.HttpUrl;
 import okhttp3.OkHttpClient;
 import org.junit.jupiter.api.BeforeAll;
@@ -13,8 +13,8 @@
 import java.io.IOException;
 
 import static com.github.tomakehurst.wiremock.client.WireMock.*;
-
-import static org.assertj.core.api.Assertions.*;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
 
 @WireMockTest
 class FeaturesEndpointTest {
@@ -149,7 +149,7 @@ void getPricingTokenByUserId() {
                 ok().withBodyFile("pricing-token-response.json")));
 
         try {
-            assertThat(endpoint.generatePricingTokenForUser(userId).length()).isEqualTo(879);
+            assertThat(endpoint.generatePricingTokenForUser(userId)).hasSize(879);
         } catch (IOException e) {
             fail();
         }
diff --git a/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionRequestTest.java b/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionRequestTest.java
index 2f29fdc..1700a93 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionRequestTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionRequestTest.java
@@ -2,10 +2,11 @@
 
 import static org.assertj.core.api.Assertions.*;
 
-import java.time.Duration;
 
 import org.junit.jupiter.api.Test;
 
+import java.util.Set;
+
 class SubscriptionRequestTest {
 
     private static final UserContact TEST_USER_CONTACT = UserContact.builder("123456789", "alexdoe")
@@ -14,7 +15,7 @@ class SubscriptionRequestTest {
     @Test
     void givenMultipleServicesInSubscriptionShouldCreate() {
 
-        long renewalDays = 30;
+        int renewalDays = 30;
         String service1Name = "Petclinic";
         String service2Name = "Petclinic Labs";
 
@@ -25,12 +26,33 @@ void givenMultipleServicesInSubscriptionShouldCreate() {
                 .builder(TEST_USER_CONTACT)
                 .subscribe(service1)
                 .subscribe(service2)
-                .renewIn(Duration.ofDays(renewalDays))
+                .renewInDays(renewalDays)
                 .build();
 
         assertThat(sub.getServices()).contains(service1, service2);
     }
 
+    @Test
+    void givenNegativeRenewalDaysShouldThrow() {
+        SubscriptionRequest.Builder builder = SubscriptionRequest
+            .builder(TEST_USER_CONTACT);
+        Set<Service> emptyServices = Set.of();
+        assertThatExceptionOfType(IllegalArgumentException.class)
+            .isThrownBy(() -> builder.renewInDays(0))
+            .withMessage("renewal period given in days must be positive");
+
+    }
+
+    @Test
+    void givenEmptyCollectionOfAddOnsShouldThrow() {
+        SubscriptionRequest.Builder builder = SubscriptionRequest
+            .builder(TEST_USER_CONTACT);
+        Set<Service> emptyServices = Set.of();
+        assertThatExceptionOfType(IllegalArgumentException.class)
+            .isThrownBy(() -> builder.subscribeAll(emptyServices))
+            .withMessage("services must not be empty");
+    }
+
     @Test
     void givenConsecutiveServiceCreationShouldThrow() {
 
@@ -89,11 +111,10 @@ void whenNoRequiredParametersInputShouldThrow() {
     void givenOptionalRenewalDaysShouldNotThrow() {
 
         SubscriptionRequest subReq = SubscriptionRequest.builder(TEST_USER_CONTACT)
-                .renewIn(null)
                 .startService("foo", "bar").plan("baz")
                 .endService().build();
 
-        assertThat(subReq.getRenewalDays()).isNull();
+        assertThat(subReq.getRenewalPeriod()).isNull();
 
     }
 
@@ -101,7 +122,6 @@ void givenOptionalRenewalDaysShouldNotThrow() {
     void givenNoEndServiceShouldThrow() {
 
         SubscriptionRequest.Builder builder = SubscriptionRequest.builder(TEST_USER_CONTACT)
-                .renewIn(null)
                 .startService("foo", "bar").plan("baz");
 
         assertThatExceptionOfType(IllegalStateException.class)
diff --git a/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionTest.java b/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionTest.java
index 95bb911..2e78487 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionTest.java
@@ -44,7 +44,8 @@ void givenSubscriptionShould() {
 
         Subscription subscription = Subscription.builder(contact, start, end, service)
             .renewInDays(renewalDays)
-            .addSnapshots(history).build();
+            .addSnapshots(history)
+            .build();
 
         assertThat(subscription.getUsername()).isEqualTo(username);
         assertThat(subscription.getStartDate()).isEqualTo(start.toLocalDateTime());
@@ -60,6 +61,69 @@ void givenSubscriptionShould() {
         assertThat(subscription.getHistory().get(0).getService(serviceName)).hasValue(snapshotService);
     }
 
+    @Test
+    void givenUsageLevelsShouldCreateSubscription() {
+
+        String petclinic = "petclinic";
+        String maxPets = "maxPets";
+        double registeredPets = 3;
+        UsageLevel ulMaxPets = UsageLevel.of(maxPets, registeredPets);
+
+        String petclinicAI = "petclinic-ai";
+        String maxTokens = "maxTokens";
+        ZonedDateTime reset = ZonedDateTime.parse("2025-02-01T00:00:00Z");
+        UsageLevel ulMaxTokens =  UsageLevel.of(maxTokens, 20, reset);
+        Map<String, Map<String, UsageLevel>> usageLevels =
+            Map.of(petclinic, Map.of(maxPets, ulMaxPets),
+                petclinicAI, Map.of(maxTokens,ulMaxTokens));
+        Subscription subscription = Subscription.builder(TEST_CONTACT, START, END, TEST_SERVICE)
+            .addUsageLevels(usageLevels)
+            .build();
+
+        assertThat(subscription.getServiceUsageLevels(petclinic)).isNotEmpty();
+        assertThat(subscription.getUsageLevel(petclinic, maxPets)).hasValue(ulMaxPets);
+    }
+
+    @Test
+    void givenNullServiceShouldBeEmptyServiceUsageLevels() {
+
+        String petclinic = "petclinic";
+        String maxPets = "maxPets";
+        double registeredPets = 3;
+        UsageLevel ulMaxPets = UsageLevel.of(maxPets, registeredPets);
+
+        Map<String, Map<String, UsageLevel>> usageLevels = Map.of(petclinic, Map.of(maxPets, ulMaxPets));
+        Subscription subscription = Subscription.builder(TEST_CONTACT, START, END, TEST_SERVICE)
+            .addUsageLevels(usageLevels)
+            .build();
+
+        assertThatExceptionOfType(NullPointerException.class)
+            .isThrownBy(() -> subscription.getServiceUsageLevels(null))
+            .withMessage("service name must not be null");
+    }
+
+    @Test
+    void givenNullUsageLimitShouldBeEmptyUsageLevel() {
+
+        String petclinic = "petclinic";
+        String maxPets = "maxPets";
+        double registeredPets = 3;
+        UsageLevel ulMaxPets = UsageLevel.of(maxPets, registeredPets);
+
+        Map<String, Map<String, UsageLevel>> usageLevels = Map.of(petclinic, Map.of(maxPets, ulMaxPets));
+        Subscription subscription = Subscription.builder(TEST_CONTACT, START, END, TEST_SERVICE)
+            .addUsageLevels(usageLevels)
+            .build();
+
+        assertThatExceptionOfType(NullPointerException.class)
+            .isThrownBy(() -> subscription.getUsageLevel(null, maxPets))
+            .withMessage("service name must not be null");
+
+        assertThatExceptionOfType(NullPointerException.class)
+            .isThrownBy(() -> subscription.getUsageLevel(petclinic, null))
+            .withMessage("usage limit name must not be null");
+    }
+
     @Test
     void givenRenewalPeriodInDaysShouldCreate() {
 
diff --git a/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionUpdateRequestTest.java b/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionUpdateRequestTest.java
index 1aee6ca..0ba58ce 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionUpdateRequestTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/contracts/SubscriptionUpdateRequestTest.java
@@ -2,6 +2,7 @@
 
 import org.junit.jupiter.api.Test;
 
+import java.util.Collection;
 import java.util.Set;
 
 import static org.assertj.core.api.Assertions.assertThat;
@@ -70,9 +71,11 @@ void givenServiceCollectionShouldCreate() {
     @Test
     void givenEmptyCollectionOfServicesShouldThrow() {
 
-        SubscriptionUpdateRequest.Builder builder = SubscriptionUpdateRequest.builder();
+        Collection<Service> emptyServices = Set.of();
+        SubscriptionUpdateRequest.Builder builder = SubscriptionUpdateRequest
+            .builder();
         assertThatExceptionOfType(IllegalArgumentException.class)
-            .isThrownBy(() -> builder.subscribeAll(Set.of()))
+            .isThrownBy(() -> builder.subscribeAll(emptyServices))
             .withMessage("services must not be empty");
     }
 }
diff --git a/space-client/src/test/java/io/github/pgmarc/space/contracts/UsageLevelTest.java b/space-client/src/test/java/io/github/pgmarc/space/contracts/UsageLevelTest.java
index 4a2ebc5..70c5331 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/contracts/UsageLevelTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/contracts/UsageLevelTest.java
@@ -1,14 +1,13 @@
 package io.github.pgmarc.space.contracts;
 
-import static org.junit.jupiter.api.Assertions.assertAll;
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import org.junit.jupiter.api.Test;
 
 import java.time.ZonedDateTime;
 
-import org.junit.jupiter.api.Test;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+import static org.junit.jupiter.api.Assertions.assertAll;
+
 
 class UsageLevelTest {
 
@@ -16,39 +15,38 @@ class UsageLevelTest {
     void givenNonRenewableUsageLimitShouldCreate() {
 
         String usageLimitName = "maxPets";
-        double consumption = 5;
+        double consumption = 0;
         UsageLevel usageLevel = UsageLevel.of(usageLimitName, consumption);
 
         assertAll(
-                () -> assertEquals(usageLimitName, usageLevel.getName()),
-                () -> assertEquals(consumption, usageLevel.getConsumption()),
-                () -> assertFalse(usageLevel.isRenewableUsageLimit()));
+                () -> assertThat(usageLevel.getName()).isEqualTo(usageLimitName),
+                () -> assertThat(usageLevel.getConsumption()).isEqualTo(consumption),
+                () -> assertThat(usageLevel.isRenewableUsageLimit()).isFalse());
     }
 
     @Test
-    void givenInvalidParamertersShouldThrow() {
+    void givenNullUsageLimitNameShouldThrow() {
 
-        String usageLimitName = "maxPets";
-        double consumption = 5;
+        assertThatExceptionOfType(NullPointerException.class)
+            .isThrownBy(() -> UsageLevel.of(null, 5))
+                .withMessage("usage limit name must not be null");
+    }
 
-        assertAll(
-                () -> assertThrows(NullPointerException.class, () -> UsageLevel.of(null, consumption)),
-                () -> assertThrows(IllegalArgumentException.class, () -> UsageLevel.of(usageLimitName, -1)));
+    @Test
+    void givenNegativeConsumptionShouldThrow() {
+        assertThatExceptionOfType(IllegalArgumentException.class)
+            .isThrownBy(() -> UsageLevel.of("maxPets", -1))
+            .withMessage("usage level consumption must be positive");
     }
 
     @Test
     void givenRenewableUsageLimitShouldCreate() {
 
-        String usageLimitName = "maxTokens";
-        double consumption = 300;
         ZonedDateTime resetTimestamp = ZonedDateTime.parse("2025-08-19T00:00:00Z");
-        UsageLevel usageLevel = UsageLevel.of(usageLimitName, consumption, resetTimestamp);
+        UsageLevel usageLevel = UsageLevel.of("maxTokens", 300, resetTimestamp);
 
-        assertAll(
-                () -> assertEquals(usageLimitName, usageLevel.getName()),
-                () -> assertEquals(consumption, usageLevel.getConsumption()),
-                () -> assertEquals(resetTimestamp.toLocalDateTime(), usageLevel.getResetTimestamp().get()),
-                () -> assertTrue(usageLevel.isRenewableUsageLimit()));
+        assertThat(usageLevel.getResetTimestamp()).hasValue(resetTimestamp.toLocalDateTime());
+        assertThat(usageLevel.isRenewableUsageLimit()).isTrue();
     }
 
 }
diff --git a/space-client/src/test/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializerTest.java b/space-client/src/test/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializerTest.java
index a633a19..f4c97f8 100644
--- a/space-client/src/test/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializerTest.java
+++ b/space-client/src/test/java/io/github/pgmarc/space/serializers/SubscriptionRequestSerializerTest.java
@@ -1,63 +1,66 @@
 package io.github.pgmarc.space.serializers;
 
-import static org.junit.jupiter.api.Assertions.assertAll;
-import static org.junit.jupiter.api.Assertions.assertEquals;
-
-import java.time.Duration;
-import java.util.Set;
-
-import org.json.JSONObject;
-import org.junit.jupiter.api.Test;
-
 import io.github.pgmarc.space.contracts.Subscription;
 import io.github.pgmarc.space.contracts.SubscriptionRequest;
 import io.github.pgmarc.space.contracts.UserContact;
+import org.json.JSONObject;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
 
 class SubscriptionRequestSerializerTest {
 
     @Test
     void givenSubscriptionRequestShouldSerialize() {
 
-        UserContact userContact = UserContact.builder("01c36d29-0d6a-4b41-83e9-8c6d9310c508", "johndoe")
-                .firstName("John")
-                .lastName("Doe")
-                .email("john.doe@my-domain.com")
-                .phone("+34 666 666 666")
-                .build();
+        UserContact userContact = UserContact
+            .builder("01c36d29-0d6a-4b41-83e9-8c6d9310c508", "johndoe")
+            .firstName("John")
+            .lastName("Doe")
+            .email("john.doe@my-domain.com")
+            .phone("+34 666 666 666")
+            .build();
 
-        String zoom = "zoom";
         String petclinic = "petclinic";
+        String petsAdoptionCentre = "petsAdoptionCentre";
+        String petclinicVersion = "2024";
+        String petclinicPlan = "GOLD";
+        String zoom = "zoom";
+        String zoomVersion = "2025";
+        String zoomPlan = "ENTERPRISE";
+        String hugeMeetings = "hugeMeetings";
+        String extraSeats = "extraSeats";
+        int renewalDays = 365;
         SubscriptionRequest subReq = SubscriptionRequest.builder(userContact)
-                .renewIn(Duration.ofDays(365))
-                .startService(zoom, "2025")
-                .plan("ENTERPRISE")
-                .addOn("extraSeats", 2)
-                .addOn("hugeMeetings", 1)
-                .endService()
-                .startService("petclinic", "2024")
-                .plan("GOLD")
-                .addOn("petsAdoptionCentre", 1)
-                .endService()
-                .build();
+            .renewInDays(renewalDays)
+            .startService(zoom, zoomVersion)
+                .plan(zoomPlan)
+                .addOn(extraSeats, 2)
+                .addOn(hugeMeetings, 1)
+            .endService()
+            .startService(petclinic, petclinicVersion)
+                .plan(petclinicPlan)
+                .addOn(petsAdoptionCentre, 1)
+            .endService()
+            .build();
 
         SubscriptionRequestSerializer serializer = new SubscriptionRequestSerializer();
         JSONObject actual = serializer.toJson(subReq);
 
-        Set<String> serviceKeys = Set.of(zoom, petclinic);
-        Set<String> addOnZoomKeys = Set.of("hugeMeetings", "extraSeats");
-        Set<String> addOnPetclinicKeys = Set.of( "petsAdoptionCentre");
-
-        Set<String> actualZoomAddOnKeys =  actual.getJSONObject(Subscription.Keys.SUBSCRIPTION_ADDONS.toString()).getJSONObject(zoom).keySet();
-        Set<String> actualPetclinicAddOnKeys =  actual.getJSONObject(Subscription.Keys.SUBSCRIPTION_ADDONS.toString()).getJSONObject(petclinic).keySet();
-
-        assertAll(
-                () -> assertEquals(serviceKeys,
-                        actual.getJSONObject(Subscription.Keys.CONTRACTED_SERVICES.toString()).keySet()),
-                () -> assertEquals(serviceKeys, actual.getJSONObject(Subscription.Keys.SUBSCRIPTION_PLANS.toString()).keySet()),
-                () -> assertEquals(serviceKeys, actual.getJSONObject(Subscription.Keys.SUBSCRIPTION_ADDONS.toString()).keySet()),
-                () -> assertEquals(addOnZoomKeys, actualZoomAddOnKeys),
-                () -> assertEquals(addOnPetclinicKeys, actualPetclinicAddOnKeys));
+        JSONObject contractedServices = actual.getJSONObject(Subscription.Keys.CONTRACTED_SERVICES.toString());
+        JSONObject subscriptionPlans = actual.getJSONObject(Subscription.Keys.SUBSCRIPTION_PLANS.toString());
+        JSONObject subscriptionAddOns = actual.getJSONObject(Subscription.Keys.SUBSCRIPTION_ADDONS.toString());
+        int actualRenewal = actual.getJSONObject(Subscription.Keys.BILLING_PERIOD.toString())
+                .getInt("renewalDays");
+        boolean actualAutoRenew = actual.getJSONObject(Subscription.Keys.BILLING_PERIOD.toString()).getBoolean("autoRenew");
 
+        assertThat(actualRenewal).isEqualTo(renewalDays);
+        assertThat(actualAutoRenew).isTrue();
+        assertThat(contractedServices.keySet()).contains(zoom, petclinic);
+        assertThat(subscriptionPlans.getString(zoom)).isEqualTo(zoomPlan);
+        assertThat(subscriptionPlans.getString(petclinic)).isEqualTo(petclinicPlan);
+        assertThat(subscriptionAddOns.getJSONObject(zoom).keySet()).contains(hugeMeetings, extraSeats);
+        assertThat(subscriptionAddOns.getJSONObject(petclinic).keySet()).contains(petsAdoptionCentre);
     }
 
 }