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Add Assert#expectThrows #1154
Add Assert#expectThrows #1154
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Original file line number | Diff line number | Diff line change |
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@@ -298,7 +298,7 @@ public static void assertArrayEquals(String message, Object[] expecteds, | |
public static void assertArrayEquals(Object[] expecteds, Object[] actuals) { | ||
assertArrayEquals(null, expecteds, actuals); | ||
} | ||
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/** | ||
* Asserts that two boolean arrays are equal. If they are not, an | ||
* {@link AssertionError} is thrown with the given message. If | ||
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@@ -313,8 +313,8 @@ public static void assertArrayEquals(Object[] expecteds, Object[] actuals) { | |
public static void assertArrayEquals(String message, boolean[] expecteds, | ||
boolean[] actuals) throws ArrayComparisonFailure { | ||
internalArrayEquals(message, expecteds, actuals); | ||
} | ||
} | ||
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/** | ||
* Asserts that two boolean arrays are equal. If they are not, an | ||
* {@link AssertionError} is thrown. If <code>expected</code> and | ||
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@@ -955,4 +955,81 @@ public static <T> void assertThat(String reason, T actual, | |
Matcher<? super T> matcher) { | ||
MatcherAssert.assertThat(reason, actual, matcher); | ||
} | ||
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/** | ||
* This interface facilitates the use of expectThrows from Java 8. It allows method references | ||
* to void methods (that declare checked exceptions) to be passed directly into expectThrows | ||
* without wrapping. It is not meant to be implemented directly. | ||
* | ||
* @since 4.13 | ||
*/ | ||
public interface ThrowingRunnable { | ||
void run() throws Throwable; | ||
} | ||
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/** | ||
* Asserts that {@code runnable} throws an exception when executed. If it does, the exception | ||
* object is returned. If it does not, an {@link AssertionError} is thrown. | ||
* | ||
* @param runnable A function that is expected to throw an exception when executed | ||
* @return The exception thrown by {@code runnable} | ||
* @since 4.13 | ||
*/ | ||
public static <T extends Throwable> T expectThrows(ThrowingRunnable runnable) { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Choose 1 . with Generics and then ThrowingRunnable and without cast, |
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return (T) expectThrows(null, Throwable.class, runnable); | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. This is an unchecked cast. If we keep this method and the one below IMHO it should rather return just There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Maybe this method and the one below should be called There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. The cast is checked at runtime, just like an explicit downcast from |
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} | ||
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/** | ||
* Asserts that {@code runnable} throws an exception when executed. If it does, the exception | ||
* object is returned. If it does not, an {@link AssertionError} is thrown with the given {@code | ||
* message}. | ||
* | ||
* @param message the identifying message for the {@link AssertionError} | ||
* @param runnable A function that is expected to throw an exception when executed | ||
* @return The exception thrown by {@code runnable} | ||
* @since 4.13 | ||
*/ | ||
public static <T extends Throwable> T expectThrows(String message, ThrowingRunnable runnable) { | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Could you explain the use case for this? When would you know a call would throw but not know or care what exception is thrown? And how would the caller specify T? There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. If I have a constructor that enforces preconditions on its arguments (e.g. no null references), I don't really care what happens when bad arguments get passed into the constructor, as long as it doesn't return normally (thereby allowing a reference to an inconsistent object to escape). It doesn't matter if the constructor throws The caller doesn't need to specify // No explicit cast takes place
NullPointerException npe = expectThrows(() -> {throw new
Assert.assertNull(npe.getMessage()); There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. You don't care if the constructor throws a If you don't care between There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. First of all, you're not objecting to my API design or my testing practices, you're objecting to catching Catching Furthermore: no, I don't care if my constructor throws Finally, even if you're very very precise in the types that you throw and catch, and you assert that (say)
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return (T) expectThrows(message, Throwable.class, runnable); | ||
} | ||
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/** | ||
* Asserts that {@code runnable} throws an exception of type {@code throwableClass} when | ||
* executed. If it does, the exception object is returned. If it does not throw an exception, an | ||
* {@link AssertionError} is thrown. If it throws the wrong type of exception, an {@code | ||
* AssertionError} is thrown describing the mismatch. | ||
* | ||
* @param throwableClass the expected type of the exception | ||
* @param runnable A function that is expected to throw an exception when executed | ||
* @return The exception thrown by {@code runnable} | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Please add There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. If 4.13 doesn't happen, will this be changed to There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Yes, we will update all of the Note one of the other maintainers might request to just have this branch target the 5.0 branch. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Since this is only really usable in the presence of JDK 8 and lambda expressions, I believe this should end up in our planned Java 8 extensions project which is codenamed junit-lambda. We've already created the repo on GitHub but the project is not set up to accept pull requests yet. There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. @marcphilipp I actually disagree we should target these changes to JUnitLambda, for two reasons. Firstly, we don't have a timeframe for the JDK 8 release. Secondly, we are deprecating Hamcrest APIs in 4.13/5.0, making |
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* @since 4.13 | ||
*/ | ||
public static <T extends Throwable> T expectThrows(Class<T> throwableClass, ThrowingRunnable runnable) { | ||
return expectThrows(null, throwableClass, runnable); | ||
} | ||
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/** | ||
* Asserts that {@code runnable} throws an exception of type {@code throwableClass} when | ||
* executed. If it does, the exception object is returned. If it does not throw an exception, an | ||
* {@link AssertionError} is thrown with the given {@code message}. If it throws the wrong type | ||
* of exception, an {@code AssertionError} is thrown describing the mismatch. | ||
* | ||
* @param message the identifying message for the {@link AssertionError} | ||
* @param throwableClass the expected type of the exception | ||
* @param runnable A function that is expected to throw an exception when executed | ||
* @return The exception thrown by {@code runnable} | ||
* @since 4.13 | ||
*/ | ||
public static <T extends Throwable> T expectThrows(String message, Class<T> throwableClass, ThrowingRunnable runnable) { | ||
try { | ||
runnable.run(); | ||
} catch (Throwable t) { | ||
String mismatchMessage = String.format("Expected %s to be thrown, but got %s instead", | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. You can avoid the formatting by calling Also, I suggest "expected %s to be thrown, but %s was thrown", and prepend "message" if it's not null, like we do in There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I don't understand this remark. What about There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Sigh. I really dislike how hard it is to follow comments on anything but the latest commit in github. :-( My point was that |
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throwableClass.getSimpleName(), t.getClass().getSimpleName()); | ||
assertTrue(mismatchMessage, throwableClass.isInstance(t)); | ||
return (T) t; | ||
} | ||
fail(message); | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. When I call There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Ok: if (message == null) {
message = String.format("Expected %s to be thrown, but nothing was thrown.", throwableClass.getSimpleName());
} |
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throw new AssertionError(); // This statement is unreachable. | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. the above two lines can be replaced by throw new AssertionError(message); There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Ah. Well, that's true now, since message can't be null. |
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} | ||
} |
Original file line number | Diff line number | Diff line change |
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@@ -11,15 +11,18 @@ | |
import static org.junit.Assert.assertSame; | ||
import static org.junit.Assert.assertThat; | ||
import static org.junit.Assert.assertTrue; | ||
import static org.junit.Assert.expectThrows; | ||
import static org.junit.Assert.fail; | ||
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import java.math.BigDecimal; | ||
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import org.junit.Assert; | ||
import org.junit.Assert.ThrowingRunnable; | ||
import org.junit.ComparisonFailure; | ||
import org.junit.Test; | ||
import org.junit.internal.ArrayComparisonFailure; | ||
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import java.io.IOException; | ||
import java.math.BigDecimal; | ||
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/** | ||
* Tests for {@link org.junit.Assert} | ||
*/ | ||
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@@ -170,7 +173,7 @@ public void oneDimensionalDoubleArraysAreNotEqual() { | |
public void oneDimensionalFloatArraysAreNotEqual() { | ||
assertArrayEquals(new float[]{1.0f}, new float[]{2.5f}, 1.0f); | ||
} | ||
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@Test(expected = AssertionError.class) | ||
public void oneDimensionalBooleanArraysAreNotEqual() { | ||
assertArrayEquals(new boolean[]{true}, new boolean[]{false}); | ||
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@@ -674,4 +677,83 @@ public void assertNotEqualsIgnoresDeltaOnNaN() { | |
public void assertNotEqualsIgnoresFloatDeltaOnNaN() { | ||
assertNotEquals(Float.NaN, Float.NaN, 1f); | ||
} | ||
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@Test(expected = AssertionError.class) | ||
public void expectThrowsRequiresAnExceptionToBeThrown() { | ||
expectThrows(nonThrowingRunnable()); | ||
} | ||
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@Test | ||
public void expectThrowsIncludesNoMessageByDefault() { | ||
try { | ||
expectThrows(nonThrowingRunnable()); | ||
} catch (AssertionError ex) { | ||
assertNull(ex.getMessage()); | ||
return; | ||
} | ||
fail(); | ||
} | ||
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@Test | ||
public void expectThrowsIncludesTheSuppliedMessage() { | ||
try { | ||
expectThrows("message", nonThrowingRunnable()); | ||
} catch (AssertionError ex) { | ||
assertEquals("message", ex.getMessage()); | ||
return; | ||
} | ||
fail(); | ||
} | ||
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@Test | ||
public void expectThrowsReturnsTheSameObjectThrown() { | ||
NullPointerException npe = new NullPointerException(); | ||
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Throwable throwable = expectThrows(throwingRunnable(npe)); | ||
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assertSame(npe, throwable); | ||
} | ||
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@Test(expected = ClassCastException.class) | ||
There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. I personally think throwing There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Now that I think about it, we should be more concerned about losing the exception that actually was caught. That's the main piece of information you would need to debug a problem in the underlying SUT. (Note that fixing this is orthogonal to whether the expected exception type is specified/required.) There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Unfortunately, the exception that was caught could be a checked exception, so if an unexpected exception is caught, we would need to do wrapping at least for checked exceptions. How about we if we catch an unexpected exception, we make that exception the cause of the Edit: Note that if we catch an unexpected unchecked exception or an unexpected error, we could just rethrow it, but then the behavior of the API would be hard to predict. And yes, I know there are hacks that allow you to throw checked exceptions from methods that don't declare them, but I'd rather not use them here :-) There was a problem hiding this comment. Choose a reason for hiding this commentThe reason will be displayed to describe this comment to others. Learn more. Yes, I've already done that. You can throw an undeclared checked exception using a technique like Lombok uses to implement |
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public void expectThrowsDetectsTypeMismatchesViaAssignment() { | ||
NullPointerException npe = new NullPointerException(); | ||
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IOException ioException = expectThrows(throwingRunnable(npe)); | ||
} | ||
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@Test(expected = AssertionError.class) | ||
public void expectThrowsDetectsTypeMismatchesViaExplicitTypeHint() { | ||
NullPointerException npe = new NullPointerException(); | ||
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expectThrows(IOException.class, throwingRunnable(npe)); | ||
} | ||
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@Test | ||
public void expectThrowsSuppliesACoherentErrorMessageUponTypeMismatch() { | ||
NullPointerException npe = new NullPointerException(); | ||
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try { | ||
expectThrows(IOException.class, throwingRunnable(npe)); | ||
} catch (AssertionError error) { | ||
assertEquals("Expected IOException to be thrown, but got NullPointerException instead", | ||
error.getMessage()); | ||
return; | ||
} | ||
fail(); | ||
} | ||
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private static ThrowingRunnable nonThrowingRunnable() { | ||
return new ThrowingRunnable() { | ||
public void run() throws Throwable { | ||
} | ||
}; | ||
} | ||
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private static ThrowingRunnable throwingRunnable(final Throwable t) { | ||
return new ThrowingRunnable() { | ||
public void run() throws Throwable { | ||
throw t; | ||
} | ||
}; | ||
} | ||
} |
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why the junit has still the same tendency to use nested interfaces and nested annotations like
Parameter
.It's really awful code like
Assert.ThrowingRunnable
and using static import forAssert.*
and much easier to use andimport ThrowingRunnable
. Bad example is to design API likeParameterized.Parameter
.The only reason why nested classes is that they are not static and share one instance; otherwise it's useless.
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There's no reason you need a star import. You can just static import
Assert.ThrowingRunnable
. Whether or not this interface should be extracted into a top-level file is up to the maintainers.There was a problem hiding this comment.
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No I dont think so it's thier decision. This is opensource and code review. The reviewer can be anyone.
The argument is that nested classes share instance; otherwise they are useless. Nested annotations/interfaces are really hard to use if you want to have nice and meaningful code.
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You can comment all you want on matters of code organization, and in accordance with Parkinson's Law of Triviality, people commonly do. My point is that the maintainers (which is not a group I belong to) have the best understanding of what the relevant convention is (if any) for new code, and what conditions would be sufficient for breaking that convention.
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I think there are cases where static nested classes make sense as a kind of organization tool to avoid an explosion of unrelated top-level classes in a package (see, for example,
Map.Entrry
).I personally haven't decided if
ThrowingRunnnable
should be a top-level class. If we think it will be used elsewhere (perhapsErrorCollector
) then it should.There was a problem hiding this comment.
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I think that
ThrowingRunnnable
is a bit of a special case because it's just a shim. It gives us a place to hang the specific functional type signature we want to accept. The interface itself is only intended to be implemented by the compiler; it's not really part of an API or SPI.There was a problem hiding this comment.
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And yet extension developers will use it when they develop more complicated APIs that reuse our code.
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Yeah, it seems like there's no way to "encapsulate" this interface. We won't be able to move, eliminate, or rename it later.
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@marcphilipp do you have thoughts about whether this should be a top-level class? If we need it in another class, or if API developers want to use our code, then they will either need to import a nested class or introduce their own version. I don't have a strong feeling, but wanted to make sure you saw this thread.