Add Jackson to test HTTP client as well

mailbox-core/build.gradle

@@ -35,6 +35,7 @@ dependencies {
     testImplementation "io.mockk:mockk:$mockk_version"
     testImplementation "ch.qos.logback:logback-classic:1.2.5"
     testImplementation "io.ktor:ktor-client-cio:$ktor_version"
+    testImplementation "io.ktor:ktor-client-jackson:$ktor_version"
     testImplementation "com.google.dagger:hilt-core:$hilt_version"
     kaptTest "com.google.dagger:dagger-compiler:$hilt_version"
 }

mailbox-core/src/test/java/org/briarproject/mailbox/core/server/IntegrationTest.kt

@@ -2,6 +2,8 @@ package org.briarproject.mailbox.core.server
 
 import io.ktor.client.HttpClient
 import io.ktor.client.engine.cio.CIO
+import io.ktor.client.features.json.JacksonSerializer
+import io.ktor.client.features.json.JsonFeature
 import org.briarproject.mailbox.core.DaggerTestComponent
 import org.briarproject.mailbox.core.TestComponent
 import org.briarproject.mailbox.core.TestModule
@@ -20,6 +22,9 @@ abstract class IntegrationTest {
     private val lifecycleManager by lazy { testComponent.getLifecycleManager() }
     protected val httpClient = HttpClient(CIO) {
         expectSuccess = false // prevents exceptions on non-success responses
+        install(JsonFeature) {
+            serializer = JacksonSerializer()
+        }
     }
     protected val baseUrl = "http://127.0.0.1:$PORT"