Eventually

Trait that provides the eventually construct, which periodically retries executing a passed by-name parameter, until it either succeeds or the configured timeout has been surpassed.

The by-name parameter "succeeds" if it returns a result. It "fails" if it throws any exception that would normally cause a test to fail. (These are any exceptions except TestPendingException and Errors listed in the Treatment of java.lang.Errors section of the documentation of trait Suite.)

For example, the following invocation of eventually would succeed (not throw an exception):

val xs = 1 to 125
val it = xs.iterator
eventually { it.next should be (3) }

However, because the default timeout is 150 milliseconds, the following invocation of eventually would ultimately produce a TestFailedDueToTimeoutException:

val xs = 1 to 125
val it = xs.iterator
eventually { Thread.sleep(50); it.next should be (110) }

Assuming the default configuration parameters, a timeout of 150 milliseconds and an interval of 15 milliseconds, were passed implicitly to eventually, the detail message of the thrown TestFailedDueToTimeoutException would look like:

The code passed to eventually never returned normally. Attempted 2 times over 166.682 milliseconds. Last failure message: 2 was not equal to 110.

The cause of the thrown TestFailedDueToTimeoutException will be the exception most recently thrown by the block of code passed to eventually. (In the previous example, the cause would be the TestFailedException with the detail message 2 was not equal to 100.)

Configuration of `eventually`

The eventually methods of this trait can be flexibly configured. The two configuration parameters for eventually along with their default values and meanings are described in the following table:

Configuration Parameter	Default Value	Meaning
`timeout`	`scaled(150 milliseconds)`	the maximum amount of time to allow unsuccessful attempts before giving up and throwing `TestFailedDueToTimeoutException`
`interval`	`scaled(15 milliseconds)`	the amount of time to sleep between each attempt

The default values of both timeout and interval are passed to the scaled method, inherited from ScaledTimeSpans, so that the defaults can be scaled up or down together with other scaled time spans. See the documentation for trait ScaledTimeSpans for more information.

The eventually methods of trait Eventually each take a PatienceConfig object as an implicit parameter. This object provides values for the two configuration parameters. (These configuration parameters are called "patience" because they determine how patient tests will be with asynchronous operations: how long they will tolerate failures before giving up and how long they will wait before checking again after a failure.) Trait Eventually provides an implicit val named patienceConfig with each configuration parameter set to its default value. If you want to set one or more configuration parameters to a different value for all invocations of eventually in a suite you can override this val (or hide it, for example, if you are importing the members of the Eventually companion object rather than mixing in the trait). For example, if you always want the default timeout to be 2 seconds and the default interval to be 5 milliseconds, you can override patienceConfig, like this:

implicit override val patienceConfig =
  PatienceConfig(timeout = scaled(Span(2, Seconds)), interval = scaled(Span(5, Millis)))

Or, hide it by declaring a variable of the same name in whatever scope you want the changed values to be in effect:

implicit val patienceConfig =
  PatienceConfig(timeout = scaled(Span(2, Seconds)), interval = scaled(Span(5, Millis)))

Passing your new default values to scaled is optional, but a good idea because it allows them to be easily scaled if run on a slower or faster system.

In addition to taking a PatienceConfig object as an implicit parameter, the eventually methods of trait Eventually include overloaded forms that take one or two PatienceConfigParam objects that you can use to override the values provided by the implicit PatienceConfig for a single eventually invocation. For example, if you want to set timeout to 5 seconds for just one particular eventually invocation, you can do so like this:

eventually (timeout(Span(5, Seconds))) { Thread.sleep(10); it.next should be (110) }

This invocation of eventually will use 5 seconds for the timeout and whatever value is specified by the implicitly passed PatienceConfig object for the interval configuration parameter. If you want to set both configuration parameters in this way, just list them separated by commas:

eventually (timeout(Span(5, Seconds)), interval(Span(5, Millis))) { it.next should be (110) }

You can also import or mix in the members of SpanSugar if you want a more concise DSL for expressing time spans:

eventually (timeout(5 seconds), interval(5 millis)) { it.next should be (110) }

Note that ScalaTest will not scale any time span that is not explicitly passed to scaled to make the meaning of the code as obvious as possible. Thus if you ask for "timeout(5 seconds)" you will get exactly that: a timeout of five seconds. If you want such explicitly given values to be scaled, you must pass them to scale explicitly like this:

eventually (timeout(scaled(5 seconds))) { it.next should be (110) }

The previous code says more clearly that the timeout will be five seconds, unless scaled higher or lower by the scaled method.

Simple backoff algorithm

The eventually methods employ a very simple backoff algorithm to try and maximize the speed of tests. If an asynchronous operation completes quickly, a smaller interval will yield a faster test. But if an asynchronous operation takes a while, a small interval will keep the CPU busy repeatedly checking and rechecking a not-ready operation, to some extent taking CPU cycles away from other processes that could proceed. To strike the right balance between these design tradeoffs, the eventually methods will check more frequently during the initial interval.

Rather than sleeping an entire interval if the initial attempt fails, eventually will only sleep 1/10 of the configured interval. It will continue sleeping only 1/10 of the configured interval until the configured interval has passed, after which it sleeps the configured interval between attempts. Here's an example in which the timeout is set equal to the interval:

val xs = 1 to 125
val it = xs.iterator
eventually(timeout(100 milliseconds), interval(100 milliseconds)) { it.next should be (110) }

Even though this call to eventually will time out after only one interval, approximately, the error message will likely report that more than one (and less than ten) attempts were made:

The code passed to eventually never returned normally. Attempted 6 times over 100.485 milliseconds. Last failure message: 6 was not equal to 110.

Note that if the initial attempt takes longer than the configured interval to complete, eventually will never sleep for a 1/10 interval. You can observe this behavior in the second example above in which the first statement in the block of code passed to eventually was Thread.sleep(50).

Usage note: `Eventually` intended primarily for integration testing

Although the default timeouts of trait Eventually are tuned for unit testing, the use of Eventually in unit tests is a choice you should question. Usually during unit testing you'll want to mock out subsystems that would require Eventually, such as network services with varying and unpredictable response times. This will allow your unit tests to run as fast as possible while still testing the focused bits of behavior they are designed to test.

Nevertheless, because sometimes it will make sense to use Eventually in unit tests (and because it is destined to happen anyway even when it isn't the best choice), Eventually by default uses timeouts tuned for unit tests: Calls to eventually are more likely to succeed on fast development machines, and if a call does time out, it will do so quickly so the unit tests can move on.

When you are using Eventually for integration testing, therefore, the default timeout and interval may be too small. A good way to override them is by mixing in trait IntegrationPatience or a similar trait of your own making. Here's an example:

class ExampleSpec extends FeatureSpec with Eventually with IntegrationPatience {
  // Your integration tests here...
}

Trait IntegrationPatience increases the default timeout from 150 milliseconds to 15 seconds, the default interval from 15 milliseconds to 150 milliseconds. If need be, you can do fine tuning of the timeout and interval by specifying a time span scale factor when you run your tests.

Source: Eventually.scala

Linear Supertypes

PatienceConfiguration, AbstractPatienceConfiguration, ScaledTimeSpans, AnyRef, Any

Known Subclasses

Eventually

Type Members

final case class PatienceConfig(timeout: Span = scaled(Span(150, Millis)), interval: Span = scaled(Span(15, Millis))) extends Product with Serializable

Configuration object for asynchronous constructs, such as those provided by traits Eventually and Waiters.
Configuration object for asynchronous constructs, such as those provided by traits Eventually and Waiters.
The default values for the parameters are:

Configuration Parameter Default Value

timeout scaled(150 milliseconds)

interval scaled(15 milliseconds)

timeout
the maximum amount of time to wait for an asynchronous operation to complete before giving up and throwing TestFailedException.
interval
the amount of time to sleep between each check of the status of an asynchronous operation when polling

Definition Classes
AbstractPatienceConfiguration

Configuration Parameter	Default Value
`timeout`	`scaled(150 milliseconds)`
`interval`	`scaled(15 milliseconds)`

Value Members

final def !=(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def ##(): Int

Definition Classes
AnyRef → Any
final def ==(arg0: Any): Boolean

Definition Classes
AnyRef → Any
final def asInstanceOf[T0]: T0

Definition Classes
Any
def clone(): AnyRef

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( ... )
final def eq(arg0: AnyRef): Boolean

Definition Classes
AnyRef
def equals(arg0: Any): Boolean

Definition Classes
AnyRef → Any
def eventually[T](fun: ⇒ T)(implicit config: PatienceConfig, pos: Position): T

Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
The by-name parameter "succeeds" if it returns a result. It "fails" if it throws any exception that would normally cause a test to fail. (These are any exceptions except TestPendingException and Errors listed in the Treatment of java.lang.Errors section of the documentation of trait Suite.)
The maximum amount of time in milliseconds to tolerate unsuccessful attempts before giving up is configured by the timeout field of the PatienceConfig passed implicitly as the last parameter. The interval to sleep between attempts is configured by the interval field of the PatienceConfig passed implicitly as the last parameter.
fun
the by-name parameter to repeatedly invoke
config
the PatienceConfig object containing the timeout and interval parameters
returns
the result of invoking the fun by-name parameter, the first time it succeeds
def eventually[T](interval: Interval)(fun: ⇒ T)(implicit config: PatienceConfig, pos: Position): T

Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
The by-name parameter "succeeds" if it returns a result. It "fails" if it throws any exception that would normally cause a test to fail. (These are any exceptions except TestPendingException and Errors listed in the Treatment of java.lang.Errors section of the documentation of trait Suite.)
The maximum amount of time in milliseconds to tolerate unsuccessful attempts before giving up is configured by the timeout field of the PatienceConfig passed implicitly as the last parameter. The interval to sleep between attempts is configured by the value contained in the passed interval parameter.
interval
the Interval configuration parameter
fun
the by-name parameter to repeatedly invoke
config
the PatienceConfig object containing the (used) timeout and (unused) interval parameters
returns
the result of invoking the fun by-name parameter, the first time it succeeds
def eventually[T](timeout: Timeout)(fun: ⇒ T)(implicit config: PatienceConfig, pos: Position): T

Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
The by-name parameter "succeeds" if it returns a result. It "fails" if it throws any exception that would normally cause a test to fail. (These are any exceptions except TestPendingException and Errors listed in the Treatment of java.lang.Errors section of the documentation of trait Suite.)
The maximum amount of time in milliseconds to tolerate unsuccessful attempts before giving up and throwing TestFailedException is configured by the value contained in the passed timeout parameter. The interval to sleep between attempts is configured by the interval field of the PatienceConfig passed implicitly as the last parameter.
timeout
the Timeout configuration parameter
fun
the by-name parameter to repeatedly invoke
config
the PatienceConfig object containing the (unused) timeout and (used) interval parameters
returns
the result of invoking the fun by-name parameter, the first time it succeeds
def eventually[T](timeout: Timeout, interval: Interval)(fun: ⇒ T)(implicit pos: Position): T

Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
Invokes the passed by-name parameter repeatedly until it either succeeds, or a configured maximum amount of time has passed, sleeping a configured interval between attempts.
The by-name parameter "succeeds" if it returns a result. It "fails" if it throws any exception that would normally cause a test to fail. (These are any exceptions except TestPendingException and Errors listed in the Treatment of java.lang.Errors section of the documentation of trait Suite.)
The maximum amount of time in milliseconds to tolerate unsuccessful attempts before giving up and throwing TestFailedException is configured by the value contained in the passed timeout parameter. The interval to sleep between attempts is configured by the value contained in the passed interval parameter.
timeout
the Timeout configuration parameter
interval
the Interval configuration parameter
fun
the by-name parameter to repeatedly invoke
returns
the result of invoking the fun by-name parameter, the first time it succeeds
def finalize(): Unit

Attributes
protected[java.lang]
Definition Classes
AnyRef
Annotations
@throws( classOf[java.lang.Throwable] )
final def getClass(): Class[_]

Definition Classes
AnyRef → Any
def hashCode(): Int

Definition Classes
AnyRef → Any
def interval(value: Span): Interval

Returns an Interval configuration parameter containing the passed value, which specifies the amount of time to sleep after a retry.
Returns an Interval configuration parameter containing the passed value, which specifies the amount of time to sleep after a retry.

Definition Classes
PatienceConfiguration
final def isInstanceOf[T0]: Boolean

Definition Classes
Any
final def ne(arg0: AnyRef): Boolean

Definition Classes
AnyRef
final def notify(): Unit

Definition Classes
AnyRef
final def notifyAll(): Unit

Definition Classes
AnyRef
implicit def patienceConfig: PatienceConfig

Implicit PatienceConfig value providing default configuration values.
Implicit PatienceConfig value providing default configuration values.
To change the default configuration, override or hide this def with another implicit PatienceConfig containing your desired default configuration values.

Definition Classes
PatienceConfiguration → AbstractPatienceConfiguration
final def scaled(span: Span): Span

Scales the passed Span by the Double factor returned by spanScaleFactor.
Scales the passed Span by the Double factor returned by spanScaleFactor.
The Span is scaled by invoking its scaledBy method, thus this method has the same behavior: The value returned by spanScaleFactor can be any positive number or zero, including a fractional number. A number greater than one will scale the Span up to a larger value. A fractional number will scale it down to a smaller value. A factor of 1.0 will cause the exact same Span to be returned. A factor of zero will cause Span.ZeroLength to be returned. If overflow occurs, Span.Max will be returned. If underflow occurs, Span.ZeroLength will be returned.

Definition Classes
ScaledTimeSpans
Exceptions thrown
IllegalArgumentException if the value returned from spanScaleFactor is less than zero
def spanScaleFactor: Double

The factor by which the scaled method will scale Spans.
The factor by which the scaled method will scale Spans.
The default implementation of this method will return the span scale factor that was specified for the run, or 1.0 if no factor was specified. For example, you can specify a span scale factor when invoking ScalaTest via the command line by passing a -F argument to Runner.

Definition Classes
ScaledTimeSpans
final def synchronized[T0](arg0: ⇒ T0): T0

Definition Classes
AnyRef
def timeout(value: Span): Timeout

Returns a Timeout configuration parameter containing the passed value, which specifies the maximum amount to wait for an asynchronous operation to complete.
Returns a Timeout configuration parameter containing the passed value, which specifies the maximum amount to wait for an asynchronous operation to complete.

Definition Classes
PatienceConfiguration
def toString(): String

Definition Classes
AnyRef → Any
final def wait(): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long, arg1: Int): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )
final def wait(arg0: Long): Unit

Definition Classes
AnyRef
Annotations
@throws( ... )

Related Docs: object Eventually | package concurrent

trait Eventually extends PatienceConfiguration

Configuration of eventually

Simple backoff algorithm

Usage note: Eventually intended primarily for integration testing

Type Members

final case class PatienceConfig(timeout: Span = scaled(Span(150, Millis)), interval: Span = scaled(Span(15, Millis))) extends Product with Serializable

Value Members

final def !=(arg0: Any): Boolean

final def ##(): Int

final def ==(arg0: Any): Boolean

final def asInstanceOf[T0]: T0

def clone(): AnyRef

final def eq(arg0: AnyRef): Boolean

def equals(arg0: Any): Boolean

def eventually[T](fun: ⇒ T)(implicit config: PatienceConfig, pos: Position): T

def eventually[T](interval: Interval)(fun: ⇒ T)(implicit config: PatienceConfig, pos: Position): T

def eventually[T](timeout: Timeout)(fun: ⇒ T)(implicit config: PatienceConfig, pos: Position): T

def eventually[T](timeout: Timeout, interval: Interval)(fun: ⇒ T)(implicit pos: Position): T

def finalize(): Unit

final def getClass(): Class[_]

def hashCode(): Int

def interval(value: Span): Interval

final def isInstanceOf[T0]: Boolean

final def ne(arg0: AnyRef): Boolean

final def notify(): Unit

final def notifyAll(): Unit

implicit def patienceConfig: PatienceConfig

final def scaled(span: Span): Span

def spanScaleFactor: Double

final def synchronized[T0](arg0: ⇒ T0): T0

def timeout(value: Span): Timeout

def toString(): String

final def wait(): Unit

final def wait(arg0: Long, arg1: Int): Unit

final def wait(arg0: Long): Unit

Inherited from PatienceConfiguration

Inherited from AbstractPatienceConfiguration

Inherited from ScaledTimeSpans

Inherited from AnyRef

Inherited from Any

Ungrouped

Configuration of `eventually`

Usage note: `Eventually` intended primarily for integration testing