If I don't actually have an explicit assertions like count must_== 1 a in Specs2 test, I'd get an error indicating no implicit could be found.
// doesn't compile
class Example extends Specification {
"You need an assertion" >> {
// hello!
}
}
Fair enough.
But if I also use scalamock's MockContext, I can rely on just expectations rather than assertions; mock something and scalamock will verify methods are called etc;
class MockExample extends Specification {
"I can use 'expectations' here instead" in new MockContext {
val foo = mock[Foo]
(foo.bar _).expects(*).once
// no explicit assertions
}
}
However, if I try and share context setup by mixing in IsolatedMockFactory, I'm back to the compiler failure. Any ideas how to fix it?
// doesn't compile
class AnotherMockExample extends Specification with IsolatedMockFactory {
val foo = mock[Foo]
"I can't use 'expectations' here any more" >> {
(foo.bar _).expects(*).once
}
}
An example in specs2 accepts anything that has an org.specs2.execute.AsResult typeclass instance. Since (foo.bar _).expects.once is of type CallHandler you can create an AsResult instance for CallHandler that just evaluates the value and returns Success
implicit def CallHandlerAsResult[R : Defaultable]: AsResult[CallHandler[R]] = new AsResult {
def asResult(c: =>CallHandler[R]) = {
c
Success
}
}
Since failures are exception-based in ScalaMock this should result in an exception being thrown if some mock expectation is not satisfied.
Related
I can extend my Scala class Foo with additional methods via an implicit class:
trait Foo {
def bar: String
}
object FooExtensions {
object implicits {
implicit class FooOps(foo: Foo) {
def baz: String = "baz"
}
}
}
But can I mock out those methods?
import org.mockito.Mockito
import org.scalatest.WordSpec
import org.scalatest.mockito.MockitoSugar
class MySpec extends WordSpec with MockitoSugar {
"My mock" should {
"handle methods from implicit classes" in {
import FooExtensions.implicits._
val foo = mock[Foo]
Mockito.when(foo.baz).thenReturn("bix") // fails at runtime
}
}
}
This compiles, but fails with
when() requires an argument which has to be 'a method call on a mock'.
For example:
when(mock.getArticles()).thenReturn(articles);
Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
Those methods *cannot* be stubbed/verified.
Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other object.
org.mockito.exceptions.misusing.MissingMethodInvocationException:
when() requires an argument which has to be 'a method call on a mock'.
For example:
when(mock.getArticles()).thenReturn(articles);
Also, this error might show up because:
1. you stub either of: final/private/equals()/hashCode() methods.
Those methods *cannot* be stubbed/verified.
Mocking methods declared on non-public parent classes is not supported.
2. inside when() you don't call method on mock but on some other object.
Is it possible to mock methods added via implicit classes? Hopefully with Mockito (or mockito-scala) but I'm interested in any approach that works.
Thing about extension methods, is that they are basically a syntactic sugar:
trait Foo
implicit class ExtensionMethods(foo: Foo) {
def bar: String = "bar
}
foo.bar
is equal to
new ExtensionMethods(foo).bar
So mocking:
Mockito.when(foo.bar).thenReturn("bix")
becomes:
Mockito.when(new ExtensionMethods(foo).bar).thenReturn("bix")
I think there is no workaround - perhaps PowerMock could let you change class constructor..., but with normal Mockito it is impossible.
Usually, it is not a problem though. That is because either:
you put into extension methods behavior, that only depends on extended value and passed parameters (and extended method is quite often pure function that doesn't require mocking) - if you want to change something there, you change input,
if behavior should change, you implement it inside a type class, and make extension method use that type class to inject behavior
trait Bar {
def bar: String
}
object Bar {
implicit val defaultBar: Bar = new Bar { def bar = "bar" }
}
implicit class ExtensionMethods(foo: Foo) {
def bar(implicit bar: Bar): String = bar.bar
}
// in test
implicit var overridenBar: Bar = ...
assert(foo.bar === "sth")
On a side note: the more functional you'll get the less you'll need to mock things as everything will depend only on input passed inside, and a cascade of mocks will become just a code smell - too tight coupling, too large interfaces, etc. Problem is that many Java libraries do not even follow SOLID principles, which makes them both hard to use/test with FP as well as bad OOP on its own. I'm telling this in case you feel mocking is the only way to go in your case.
The only way to achieve that is to use implicit conversions rather than implicit classes
This is a hack intended to show how this could be achieved, but I'd urge to take a look at the code and see why you actually need to do this
So, following your example, you could modify the code to look like this
trait Foo {
def bar: String
}
object FooExtensions {
object implicits {
implicit fooToOps(foo: Foo): FooOps = new FooOps(foo)
class FooOps(foo: Foo) {
def baz: String = "baz"
}
}
}
and your test
import org.scalatest.WordSpec
import org.mockito.MockitoSugar
class MySpec extends WordSpec with MockitoSugar {
"My mock" should {
"handle methods from implicit classes" in {
val fooOps = mock[FooOps]
implicit fooToOps(foo: Foo): FooOps = fooOps
val foo = mock[Foo]
when(foo.baz) thenReturn "bix" // works
}
}
}
the other thing to consider is that in your production you need to get an implicit parameter of the shape Foo => FooOps so when you call that method from the test the actual implicit mock is provided...
As I said, you can make it work like this, but I agree with Mateusz that you shouldn't need to
So I have the following bit of code
class MetricsLogger {
def measure[T](name:String)(operation: => T): T = {
val startTime = System.currentTimeMillis
val result = try {
operation
} finally {
logMetric(Metric(name, System.currentTimeMillis - startTime, StandardUnit.Milliseconds))
}
result
}
}
Where log Metric is some kind of side effect (e.g. upload metric to cloudwatch).
Now I am doing this like
def measuredOp = measure("metricName") { someOperation }
Here some operation is making some network calls.
Now I have to stub measured op.
So my stub is as the follows:-
val loggingMetrics = mock[MetricsLogger] // mock is from MockitoSugar trait
and my stubbing is like
Mockito.when(loggingMetrics.measure(Matchers.anyString())(Matchers.anyObject())).thenReturn(???)
So obviously my stubbing is wrong, but I cannot figure how to stub this properly.
Mockito doesn't support that as by-name parameters it's a concept that doesn't exists in Java, however, mockito-scala does support this from version 0.4.0 (try 0.4.0 or 0.4.2, ignore 0.4.1)
I just run a quick test like this
import org.mockito.{ MockitoSugar, ArgumentMatchersSugar }
class StackOverflowTest extends WordSpec with MockitoSugar with scalatest.Matchers with ArgumentMatchersSugar {
"mock[T]" should {
"it should work with by-name params" in {
val loggingMetrics = mock[MetricsLogger]
when(loggingMetrics.measure(any)(any)).thenReturn("it worked!")
loggingMetrics.measure("test")("") shouldBe "it worked!"
}
}
}
Disclaimer: I'm a maintainer of that library although it's part of the official Mockito suite
I am trying to test
trait Name extends Helper {
def name() = {
var s = getSystem()
s.name()
}
}
where all I want to do is make sure that the "s.name()" method is invoked once by mocking an instance of s, which is a System.
Helper is defined as so:
trait Helper {
def getSystem() : System = {
systemGetter.get()
}
}
As of now, my NameSpec looks something like:
class NameSpec extends FlatSpec with Matchers with MockitoSugar {
class NameImpl extends Name
var toTest = new NameImpl
val mockSystem = mock[System]
it should "call s.name() once" in {
when(getSystem() is invoked, return a mockSystem)
toTest.name()
// Verify that mockSystem.name() happened only once
}
}
What I'm confused about is how to return a mock System in toTest.name() when it calls getSystem() so that I can verify that the system calls s.name() only once. I could easily mock this System if it were a parameter to the name() method in Name trait, so I guess I don't know how to "inject" a mockSystem to be used instead of a real system when that method is invoked.
Unfortunately your code is not compilable and thus is obviously an inadequate representation of what you really have. Particularly it is not clear how the Helper really gets an object of type System. I think that in the real code you should mock the systemGetter, that I suppose is somehow injected into the objects implementing Helper trait, to return your mockSystem. However it is hard to show you a valid example of that basing on the code you provided. If for some reason this is not what you can do, there are a few more avenues.
You seem to use something like Cake pattern around Helper and its inheritance. If so, you can use a class instead of NameImpl to inject System:
class NameWithInjectedSystem(val system: System) extends Name {
override def getSystem(): System = system
}
it should "call s.name() once" in {
val mockSystem = mock[System]
val nameToTest = new NameWithInjectedSystem(mockSystem)
val mockName = "Mock name"
when(mockSystem.name()).thenReturn(mockName)
val actual = nameToTest.name()
actual should === (mockName)
verify(mockSystem, times(1)).name()
}
Finally you can mock even nameToTest object itself but this is not the way I'd suggest because it binds test to much more implementation details than you should want:
it should "call s.name() once" in {
val mockSystem = mock[System]
val nameToTest = mock[NameImpl]
when(nameToTest.getSystem()).thenReturn(mockSystem)
when(nameToTest.name()).thenCallRealMethod()
val mockName = "Mock name"
when(mockSystem.name()).thenReturn(mockName)
val actual = nameToTest.name()
actual should ===(mockName)
verify(mockSystem, times(1)).name()
}
Note how you must call thenCallRealMethod for the .name() call and so you should do for all the calls inside the name or the test will not work.
I'm using Scala 2.10, specs2 and Mockito. I want to mock scala.io.Source.fromURL(). The issue seems to be fromURL() is a function in io.Source's object.
val m = mock[io.Source]
m.fromURL returns io.Source.fromString("Some random string.")
It's a pretty straightforward mock in an Unit test. Why isn't it working?
Thanks!
Instead of mocking it, you could try spying it as follows:
val m = spy(io.Source)
Or you could mock it as follows:
val m = mock[io.Source.type]
But then how are you using Source in the class you are testing? If you had an example class like so:
class MyClass{
def foo = {
io.Source.doSomething //I know doSomething is not on Source, call not important
}
}
Then in order to take advantage of mocking/spying, you'd have to structure your class like so:
class MyClass{
val source = io.Source
def foo = {
source.doSomething
}
}
And then your test would have to look something like this:
val mockSource = mock[io.Source.type]
val toTest = new MyClass{
override val source = mockSource
}
In the Java world, static methods are the bane of mocking. In the Scala world, calls to objects can also be troublesome to deal with for unit tests. But if you follow the code above, you should be able to properly mock out an object based dependency in your class.
Good news! With the latest 1.16 release of mockito-scala, you can now mock scala objects.
To enable withObjectMocked feature, it is mandatory to create the file src/test/resources/mockito-extensions/org.mockito.plugins.MockMaker containing a single line:
mock-maker-inline
Example:
object FooObject {
def simpleMethod: String = "not mocked!"
}
"mock" should {
"stub an object method" in {
FooObject.simpleMethod shouldBe "not mocked!"
withObjectMocked[FooObject.type] {
FooObject.simpleMethod returns "mocked!"
//or
when(FooObject.simpleMethod) thenReturn "mocked!"
FooObject.simpleMethod shouldBe "mocked!"
}
FooObject.simpleMethod shouldBe "not mocked!"
}
}
See: https://github.com/mockito/mockito-scala#mocking-scala-object
Years later, above answer doesn't work as others have pointed out.
And you cannot mock the scala.io.Source object.
Can I mock final / private methods or classes? This is not supported, as mocks generated with macros are implemented as subclasses of the type to mock. So private and final methods cannot be overridden. You may want to try using an adapter or façade in your code to make it testable. It is better to test against a trait/interface instead of a concrete implementation. There are libraries that support this kind of mocking, such as PowerMock. Be aware that this kind of mocking involves Bytecode manipulation, which has the risk that your test double diverges from the actual implementation.
So what I did is an work around to abstract out scala.io.Source.fromUrl() as a function argument and pass in mocked function in tests.
// original func
def aFuncThatUsesSource() = {
val source = scala.io.Source("127.0.0.1:8080/...")
val result = source.mkString
Try(source.close())
result
}
// test friendly func that accepts `scala.io.Source.fromURL` as arg
def aTestFriendlyFunc(makeApiCall: String => BufferedSource) = {
val source = makeApiCall("127.0.0.1:8080/...")
val result = source.mkString
Try(source.close())
result
}
....
// test spec
def testyMcTesterson = () => {
val makeApiCall = mockFunction[String, BufferedSource]
makeApiCall.expects("something...")
.returns( new BufferedSource(new ByteArrayInputStream("returns something".getBytes)) )
aTestFriendlyFunc(makeApiCall) shouldEqual "returns something"
}
I am using mockito and trying to mock a scala object.
object Sample { }
//test
class SomeTest extends Specification with ScalaTest with Mockito {
"mocking should succeed" in {
val mockedSample = mock[Sample]
}
}
This gives me two compilation errors.
error: Not found type Sample
error: could not find implicit value for parameter m:
scala.reflect.ClassManifest[<error>]
If I change Sample from object to class it works.
Is is possible to mock scala objects with mockito? If yes how?
As written, your Sample is a pure singleton. Its type is its own and there is only one member of that type, period. Scala objects can extend another class (possibly abstract, if it supplies the necessary definitions to make it a concrete) and traits. Doing that gives it a type identity that includes those ancestors.
I don't know what Mockito is really doing, but to my mind, what you're asking for is strictly at odds with what a Scala object is.
Keep in mind that you can mock the methods of an object if you lift them to functions.
case class Person(name: String)
object Person {
def listToJson(lp: List[Person]) = "some actual implementation"
}
class ClassUnderTest(listToJson: (List[Person]) => String = Person.listToJson(_)) {
def testIt(lp: List[Person]) = listToJson(lp)
}
import org.specs._
import org.specs.mock.Mockito
import org.mockito.Matchers._
class ASpec extends Specification with Mockito {
"a thing" should {
"do whatever" in {
val m = mock[(List[Person]) => String]
val subject = new ClassUnderTest(m)
m(Nil) returns "mocked!"
subject.testIt(Nil) must_== "mocked! (this will fail on purpose)"
}
}
}
Here I'm not mocking the object Person, but the method on it (which is probably what the OP was intending).
The test result shows the mocking works:
[info] == ASpec ==
[error] x a thing should
[error] x do whatever
[error] 'mocked![]' is not equal to 'mocked![ (this will fail on purpose)]' (ASpec.scala:21)
[info] == ASpec ==
Meanwhile, the production-time usage of the ClassUnderTest is simply new ClassUnderTest due to the injected function being a default argument.
Since version 1.16.0 of mockito-scala it is possible to mock Scala objects, you can check the docs here, but this is an example of how it would look like.
object FooObject {
def simpleMethod: String = "not mocked!"
}
"mock" should {
"stub an object method" in {
FooObject.simpleMethod shouldBe "not mocked!"
withObjectMocked[FooObject.type] {
FooObject.simpleMethod returns "mocked!"
//or
when(FooObject.simpleMethod) thenReturn "mocked!"
FooObject.simpleMethod shouldBe "mocked!"
}
FooObject.simpleMethod shouldBe "not mocked!"
}
}
I've recently released ScalaMock, a mocking library for Scala that can, among other things, mock singleton (and companion) objects.