trait BeMatcher[-T] extends (T) => MatchResult
Trait extended by matcher objects, which may appear after the word be
, that can match a value of the specified type.
The value to match is passed to the BeMatcher
's apply
method. The result is a MatchResult
.
A BeMatcher
is, therefore, a function from the specified type, T
, to a MatchResult
.
Although BeMatcher
and Matcher
represent very similar concepts, they have no inheritance relationship
because Matcher
is intended for use right after should
or must
whereas BeMatcher
is intended for use right after be
.
As an example, you could create BeMatcher[Int]
called odd
that would match any odd Int
, and one called even
that would match
any even Int
.
Given this pair of BeMatcher
s, you could check whether an Int
was odd or even with expressions like:
num should be (odd) num should not be (even)
Here's is how you might define the odd and even BeMatchers
:
trait CustomMatchers {
class OddMatcher extends BeMatcher[Int] { def apply(left: Int) = MatchResult( left % 2 == 1, left.toString + " was even", left.toString + " was odd" ) } val odd = new OddMatcher val even = not (odd) }
// Make them easy to import with: // import CustomMatchers._ object CustomMatchers extends CustomMatchers
These BeMatcher
s are defined inside a trait to make them easy to mix into any
suite or spec that needs them.
The CustomMatchers
companion object exists to make it easy to bring the
BeMatcher
s defined in this trait into scope via importing, instead of mixing in the trait. The ability
to import them is useful, for example, when you want to use the matchers defined in a trait in the Scala interpreter console.
Here's an rather contrived example of how you might use odd
and even
:
class DoubleYourPleasureSuite extends FunSuite with MustMatchers with CustomMatchers {
def doubleYourPleasure(i: Int): Int = i * 2
test("The doubleYourPleasure method must return proper odd or even values")
val evenNum = 2 evenNum must be (even) doubleYourPleasure(evenNum) must be (even)
val oddNum = 3 oddNum must be (odd) doubleYourPleasure(oddNum) must be (odd) // This will fail } }
The last assertion in the above test will fail with this failure message:
6 was even
For more information on MatchResult
and the meaning of its fields, please
see the documentation for MatchResult
. To understand why BeMatcher
is contravariant in its type parameter, see the section entitled "Matcher's variance" in the
documentation for Matcher
.
- Self Type
- BeMatcher[T]
- Source
- BeMatcher.scala
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- BeMatcher
- Function1
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Abstract Value Members
- abstract def apply(left: T): MatchResult
Check to see if the specified object,
left
, matches, and report the result in the returnedMatchResult
.Check to see if the specified object,
left
, matches, and report the result in the returnedMatchResult
. The parameter is namedleft
, because it is usually the value to the left of ashould
ormust
invocation. For example, in:num should be (odd)
The
be (odd)
expression results in a regularMatcher
that holds a reference toodd
, theBeMatcher
passed tobe
. Theshould
method invokesapply
on this matcher, passing innum
, which is therefore the "left
" value. The matcher will passnum
(theleft
value) to theBeMatcher
'sapply
method.- left
the value against which to match
- returns
the
MatchResult
that represents the result of the match
- Definition Classes
- BeMatcher → Function1
Concrete 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
- def andThen[A](g: (MatchResult) => A): (T) => A
- Definition Classes
- Function1
- Annotations
- @unspecialized()
- final def asInstanceOf[T0]: T0
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- def clone(): AnyRef
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- protected[lang]
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- @throws(classOf[java.lang.CloneNotSupportedException]) @native()
- def compose[U](g: (U) => T): BeMatcher[U]
Compose this
BeMatcher
with the passed function, returning a newBeMatcher
.Compose this
BeMatcher
with the passed function, returning a newBeMatcher
.This method overrides
compose
onFunction1
to return a more specific function type ofBeMatcher
. For example, given anodd
matcher defined like this:val odd = new BeMatcher[Int] { def apply(left: Int) = MatchResult( left % 2 == 1, left.toString + " was even", left.toString + " was odd" ) }
You could use
odd
like this:3 should be (odd) 4 should not be (odd)
If for some odd reason, you wanted a
BeMatcher[String]
that checked whether a string, when converted to anInt
, was odd, you could make one by composingodd
with a function that converts a string to anInt
, like this:val oddAsInt = odd compose { (s: String) => s.toInt }
Now you have a
BeMatcher[String]
whoseapply
method first invokes the converter function to convert the passed string to anInt
, then passes the resultingInt
toodd
. Thus, you could useoddAsInt
like this:"3" should be (oddAsInt) "4" should not be (oddAsInt)
- Definition Classes
- BeMatcher → Function1
- final def eq(arg0: AnyRef): Boolean
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- def equals(arg0: AnyRef): Boolean
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- def finalize(): Unit
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- final def ne(arg0: AnyRef): Boolean
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- final def wait(): Unit
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