The document discusses testing Cassandra applications and introduces Stubbed Cassandra, a tool for testing Cassandra drivers. Stubbed Cassandra allows priming a fake Cassandra server to return expected responses or errors. It can be used to test failure scenarios, edge cases, and retry policies. The tool has Java and REST APIs and makes it possible to quickly test Cassandra applications in a deterministic and non-brittle way.

1. Testing
Cassandra
Applications
Christopher Batey
@chbatey

2. @chbatey
Overview
● Cassandra overview
● Cassandra failure scenarios e.g ReadTimeout,
WriteTimeout, Unavailable
● Existing technologies:
○ CCM
○ Cassandra Unit
○ Integration tests
● Stubbed Cassandra

3. @chbatey
Sleeping is good

4. @chbatey
Single node
S

5. @chbatey
More realistic

6. Tunable consistency
● Each write/read is done at a consistency
● ANY, ONE, TWO, THREE, QUORUM,
LOCAL_QUORUM, EACH_QUORUM, ALL
● Any more than ANY and ONE require a
cluster of more than one node to make
sense
@chbatey

7. Read and write timeouts
@chbatey

8. @chbatey
Unavailable

9. Unit & Integration testing
● Requirements:
@chbatey
○ Quick to run
○ Deterministic
○ Not brittle!!
● Integration tests against an embedded Cassandra? E.g.
cassandra-unit
● Integration tests against an external Cassandra running on
developer / CI machines
● Mocking the driver
S

10. Acceptance testing
@chbatey

11. How do this if it was a HTTP service?
● Release it - great book
● Wiremock - mocking HTTP services
● Saboteur - adding network latency
@chbatey

12. Stubbed Cassandra
@chbatey

13. Some code that needs testing
@chbatey
public List<Person> retrieveNames() {
ResultSet result;
try {
Statement statement = new SimpleStatement("select * from person");
statement.setConsistencyLevel(ConsistencyLevel.QUORUM);
result = session.execute(statement);
} catch (ReadTimeoutException e) {
throw new UnableToRetrievePeopleException();
}
List<Person> people = new ArrayList<>();
for (Row row : result) {
people.add(new Person(row.getString("first_name"), row.getString("last_name")));
}
return people;
}

14. The Java API
● Wraps Stubbed Cassandra
● With a method call can:
○ Create and start an instance
○ Stop an instance
○ Prime to behave in a certain way
○ Verify interactions
@chbatey

15. Starting Scassandra
@BeforeClass
public static void startScassandraServer() throws Exception {
// can override port, listen address
scassandra = ScassandraFactory.createServer();
scassandra.start();
primingClient = scassandra.primingClient();
activityClient = scassandra.activityClient();
@chbatey
}

16. @chbatey
Priming Client
public void primeQuery(PrimingRequest primeRequest)
public void primePreparedStatement(PrimingRequest primeRequest)
public List<PrimingRequest> retrievePreparedPrimes()
public List<PrimingRequest> retrieveQueryPrimes()
● Priming Request:
○ Query
○ Consistency(s)
○ Rows
○ Column Types
○ Result e.g. Success, Readtimeout, Writetimeout, Unavailable
○ Variable types (for prepared statements)

17. @chbatey
Activity client
public List<Query> retrieveQueries()
public List<Connection> retrieveConnections()
public List<PreparedStatementExecution> retrievePreparedStatementExecutions()
public void clearConnections()
public void clearQueries()
public void clearPreparedStatementExecutions()
public void clearAllRecordedActivity()
● Query has text and consistency
● Prepared statement has text, consistency and the
bound variables

18. Verifying query consistency
public void testQueryIssuedWithCorrectConsistency() {
Query expectedQuery = Query.builder()
.withQuery("select * from person")
.withConsistency("QUORUM").build();
@chbatey
underTest.retrieveNames();
List<Query> queries = activityClient.retrieveQueries();
assertTrue("Expected query with consistency QUORUM, found following queries: "
+ queries,
queries.contains(expectedQuery));
}

19. Testing behaviour
public void testRetrievingOfNames() throws Exception {
Map<String, ? extends Object> row = ImmutableMap.of(
@chbatey
"first_name", "Chris",
"last_name", "Batey");
PrimingRequest singleRowPrime = queryBuilder()
.withQuery("select * from person")
.withRows(row)
.build();
primingClient.primeQuery(singleRowPrime);
List<Person> names = underTest.retrieveNames();
assertEquals(1, names.size());
assertEquals("Chris", names.get(0).getFirstName());
}

20. @chbatey
Testing errors
@Test(expected = UnableToRetrievePeopleException.class)
public void testHandlingOfReadRequestTimeout() throws Exception {
PrimingRequest primeReadRequestTimeout = queryBuilder()
.withQuery("select * from person")
.withResult(Result.read_request_timeout)
.build();
primingClient.primeQuery(primeReadRequestTimeout);
underTest.retrieveNames();
}

21. Testing retry policies
public void testRetriesConfiguredNumberOfTimes() throws Exception {
PrimingRequest readtimeoutPrime = PrimingRequest.queryBuilder()
.withQuery("select * from person")
.withResult(Result.read_request_timeout)
.build();
primingClient.primeQuery(readtimeoutPrime);
activityClient.clearAllRecordedActivity();
@chbatey
try {
underTest.retrieveNames();
} catch (UnableToRetrievePeopleException e) {}
assertEquals(CONFIGURED_RETRIES + 1, activityClient.retrieveQueries().size());
}

22. But.. I don’t like Java
@chbatey

23. The REST API - priming
{
"when": {
"query" :"select * from person", "consistency" : ["ONE", "TWO"]
},
"then": {
"rows" :[{"first_name": "Chris", "last_name": "Batey"},
{"first_name": "Mansoor", "last_name": "Panda"},
{"first_name" : "Wayne", "last_name": "Rooney"}] ,
"column_types" : { "last_name" : "text"},
"result" : "success"
}
}
@chbatey

24. The REST API - Activity
[{
"query": "SELECT * FROM system.schema_columns",
"consistency": "ONE"
}, {
"query": "SELECT * FROM system.peers",
"consistency": "ONE"
}, {
"query": "SELECT * FROM system.local WHERE key='local'",
"consistency": "ONE"
}, {
"query": "use people",
"consistency": "ONE"
}, {
"query": "select * from people",
"consistency": "TWO"
}]
@chbatey

25. Priming prepared statements
{
"when":{
"query":"insert into people(first_name, last_name) values (?,?)"
},
"then":{
"variable_types":[
@chbatey
"ascii",
"text"
],
"result" : "success"
}
}

26. @chbatey
Priming errors
{
"when": {
"query" :"select * from people where name = ?"
},
"then": {
"result" : "read_request_timeout"
}
}

27. Priming cluster name
@chbatey
{
"when": {
"query": "SELECT * FROM system.local WHERE key='local'"
},
"then": {
"rows": [
{
"cluster_name": "custom cluster name",
"partitioner": "org.apache.cassandra.dht.Murmur3Partitioner",
"data_center": "dc1",
"rack": "rc1",
"tokens": [
"1743244960790844724"
],
"release_version": "2.0.1"
}
],
"result": "success",
"column_types": {
"tokens": "set"
}
}
}

28. What else can I do?
● Start as many instances as you like in the
same JVM
● Prime all primitive types
● Prime sets and lists of type text
● Prime prepared statements
● Verify number of connections your
application makes
@chbatey

29. Future features
● Regular expressions for the query
● Loading of schema for priming prepared
statements
● Pretending to be multiple nodes
@chbatey

30. How does this work?
● Server implemented in Scala
● Binary port for your Cassandra application to
connect to
● Admin port for the REST API
● Thin Java wrapper to make it easy to be
used in JUnit tests
@chbatey

31. How do I get it?
● It is on maven central
<dependency>
<groupId>org.scassandra</groupId>
<artifactId>java-client</artifactId>
<version>0.2.1</version>
<scope>test</scope>
</dependency>
● Or go to www.scassandra.org
○ Executable jar + REST API
@chbatey

32. @chbatey
I want to help
● Server:
○ https://github.com/scassandra/scassandra-server
● Client:
○ https://github.com/chbatey/scassandra-java-client
● Tests:
○ https://github.com/scassandra/scassandra-it-java-driver-
1

33. Summary
● Testing is good - I want more tools to help
me
● Existing tools for Cassandra are great at
happy path scenarios
● Stubbed Cassandra allows testing of edge
cases
@chbatey

34. The end - Questions?
www.scassandra.org
http://christopher-batey.blogspot.co.uk/
@chbatey
@chbatey