MongoDB

dev.rightsize.modules.MongoDBContainer — a single-node MongoDB container, always booted as a one-member replica set (required for transactions and change streams). The replica set is initiated and a primary confirmed elected before start() returns, so connectionString is immediately usable — you never need to handle the not-yet-a-primary window yourself.

Defaults

Default image	mongo:8.0
Exposed port	27017
Command	mongod --replSet docker-rs --bind_ip_all
Wait strategy	Wait.forListeningPort(), followed by a post-start replica-set-init hook

Helpers

Member	Returns
connectionString: String	A mongodb:// connection string for the test database, with directConnection=true
replicaSetUrl: String	Alias for connectionString — the container is always a (single-node) replica set

Example

package dev.rightsize.modules

import com.mongodb.client.MongoClients
import dev.rightsize.modules.MongoDBContainer
import org.bson.Document
import org.junit.jupiter.api.Assertions.assertEquals
import org.junit.jupiter.api.Test

class MongoDBContainerTest {
    @Test
    fun `inserts and counts a document`() {
        val mongo = MongoDBContainer()
        mongo.start()
        try {
            MongoClients.create(mongo.connectionString).use { client ->
                val col = client.getDatabase("test").getCollection("t")
                col.insertOne(Document("x", 1))
                assertEquals(1, col.countDocuments())
            }
        } finally {
            mongo.stop()
        }
    }
}

Backend notes

After the container reports a listening port, this module runs rs.initiate() (via execInContainer, retrying to ride out the same proxy-accepts-before-mongod-listens race described in Wait Strategies), then polls db.hello().isWritablePrimary until it returns true — up to 60 seconds, polling every 500ms. Only once a primary is confirmed elected does start() return. This two-stage approach (raw port ready, then a domain-specific liveness check before handing control back to your test) is the same shape PinotContainer uses for its /health-then-schema-POST race — see Apache Pinot for that parallel case.