How to create nested matcher

[Tedd]

I have a matcher that checks a list over a range for a certain value
[code]
package hamcrest;

import java.util.List;

import org.hamcrest.Description;
import org.hamcrest.Factory;
import org.junit.matchers.TypeSafeMatcher;


public class HasValueInRange extends TypeSafeMatcher<List<? extends
Object>> {
private final Object value;
private final int from;
private final int to;

private HasValueInRange(Object value, int from, int to) {
this.value = value;
this.from = from;
this.to = to;
}

public void describeTo(Description description) {
// TODO Auto-generated method stub
}

@Override
public boolean matchesSafely(List<? extends Object> values) {
// Verify range is valid and in array
if (from > to || to > values.size()) {
return false;
}

for (int i = from; i < to; i++) {
// If I am not equal I am done return false
if (!values.get(i).equals(value)) {
return false;
}
}

return true;
}

@Factory
public static HasValueInRange hasValueInRange(Object value, int from,
int to) {
return new HasValueInRange(value, from, to);
}

}
[/code]

I am using it as follows:
[code]
List<String> test= Arrays.asList(new String[]
{"Hello","Hello","Hello","Goodbye"});
assertThat(test, hasValueInRange("Hello", 0, 2); // This will pass
assertThat(test, hasValueInRange("Hello", 0, 3); // fail last element
is "Goodbye"
[/code]

This works great, however I would really like to be more expressive
and write the assert using nested Matchers, i.e.
[code]
List<String> test= Arrays.asList(new String[]
{"Hello","Hello","Hello","Goodbye"});
assertThat(test, hasValue("Hello", inRange(0, 2)); // This will pass
assertThat(test, hasValue("Hello", inRange(0, 3)); // fail last
element is "Goodbye"
[/code]

So I want to pass an inRange matcher to the hasValue matcher. I am
really struggling on how do implement this. I am just playing with
hamcrest and trying to learn, thanks for any help!

[Nat Pryce]

Hi.  It'll probably be easier the other way.  E.g. hasRange(5. 10. hasItem(equalTo("foo"));


The hasRange function would have the following signature:
    Matcher<List<T>> hasRange(int begin, int end, Matcher<? super List<T>> sublistMatcher)

The sublist matcher matches the sublist of the matched list between begin and end.  You can then use existing Hamcrest matchers to match a sublist that contains an element that matches some other criteria.  In the example above, it matches a sublist that contains an item equal to "foo".

Does that make sense?

    --Nat.

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[Billy Newman]

A little, but I am still very confused.

I am having a really hard time writing this matcher.

import java.util.List;

import org.hamcrest.Description;

import org.hamcrest.Factory;

import org.hamcrest.Matcher;

import org.junit.internal.matchers.TypeSafeMatcher;

public class HasRangeMatcher<T> extends TypeSafeMatcher<Matcher<List<T>>>{

private final int from;

private final int to;

private final Matcher<? super List<T>> matcher;

public HasRangeMatcher(int from, int to, Matcher<? super List<T>> matcher) {

this.from = from;

this.to = to;

this.matcher = matcher;

}

@Override

public void describeTo(Description arg0) {

}

@Override

public boolean matchesSafely(Matcher<List<T>> arg0) {

// TODO Auto-generated method stub

return false;

}

@Factory

public static <T> HasRangeMatcher<T> hasRange(int from, int to, Matcher<? super List<T>> matcher) {

return new HasRangeMatcher<T>(from, to, matcher);

}

}

I am not sure if this is what you meant.....but I have no idea how to write the matchesSafely method.  I.E. how do I iterate over a collection of elements and determine if each on matches?

[Nat Pryce]

You don't need to iterate over the elements. The Matchers.hasItem matcher already does that for you, so you can pass that to the constructor.  Then the matchesSafely method is just:

public boolean matchesSafely(Matcher<List<T>> arg0) {

return matcher.matches(arg0.subList(from,to));;

}

(And then some renaming to make it easier to understand).

Cheers,

     --Nat

[Billy Newman]

Ok I made a few mistakes that I fixed but I still cannot get this to compile:

import static org.junit.Assert.assertThat;

import static org.junit.matchers.JUnitMatchers.hasItem;

import java.util.Arrays;

import java.util.List;

import org.hamcrest.Description;

import org.hamcrest.Factory;

import org.hamcrest.Matcher;

import org.junit.internal.matchers.TypeSafeMatcher;

public class HasRangeMatcher<T> extends TypeSafeMatcher<List<T>>{

private final int from;

private final int to;

private final Matcher<? super List<T>> matcher;

public HasRangeMatcher(int from, int to, Matcher<? super List<T>> matcher) {

this.from = from;

this.to = to;

this.matcher = matcher;

}

@Override

public void describeTo(Description arg0) {

}

@Override

public boolean matchesSafely(List<T> list) {

// TODO Auto-generated method stub

return matcher.matches(list.subList(from, to));

}

@Factory

public static <T> HasRangeMatcher<List<T>> hasRange(int from, int to, Matcher<? super List<T>> matcher) {

return new HasRangeMatcher(from, to, matcher);

}

public static void main(String[] args) {

List<Integer> ints = Arrays.asList(new Integer[] {1,1,1,2,2,2,3,3,3});

assertThat(ints, hasRange(0,2, hasItem(1)));

}

}

my assertThat line does not compile,  and I cannot add a generic type to the new HasRangeMatcher I return in my factory method.

Can someone throw this into eclipse and check it out?

[Nat Pryce]

Which version of Hamcrest are you using?