Java JUnit - AssertTrue vs AssertFalse

Question

I m pretty new to Java and am following the Eclipse Total Beginner s Tutorials  They are all very helpful  but in Lesson 12  he uses assertTrue for one test case and assertFalse for another  Here s the code      Check the book out to p1  Thomas     Check to see that the book was successfully checked out to p1  Thomas  assertTrue  Book did not check out correctly   ml checkOut b1  p1          If checkOut fails  display message assertEquals  Thomas   b1 getPerson   getName      assertFalse  Book was already checked out   ml checkOut b1 p2              If checkOut fails  display message assertEquals  Book was already checked out   m1 checkOut b1 p2      I have searched for good documentation on these methods  but haven t found anything  If my understanding is correct  assertTrue as well as assertFalse display the string when the second parameter evaluates to false  If so  what is the point of having both of them   Edit  I think I see what was confusing me  The author may have put both of them in just to show their functionality  it IS a tutorial after all   And he set up one which would fail  so that the message would print out and tell me WHY it failed  Starting to make more sense   I think that s the explanation  but I m not sure

User · Answer

Your first reaction to these methods is quite interesting to me. I will use it in future arguments that both assertTrue and assertFalse are not the most friendly tools. If you would use

assertThat(thisOrThat, is(false));

it is much more readable, and it prints a better error message too.

User · Answer

The point is semantics  In assertTrue  you are asserting that the expression is true  If it is not  then it will display the message and the assertion will fail  In assertFalse  you are asserting that an expression evaluates to false  If it is not  then the message is displayed and the assertion fails   assertTrue  message  value    false     assertFalse  message  value     These are functionally the same  but if you are expecting a value to be false then use assertFalse  If you are expecting a value to be true  then use assertTrue

User · Answer

I think it s just for your convenience  and the readers of your code   Your code  and your unit tests should be ideally self documenting which this API helps with   Think abt what is more clear to read   AssertTrue   a  gt  3      or  AssertFalse a  gt  3     When you open your tests after xx months when your tests suddenly fail  it would take you much less time to understand what went wrong in the second case  my opinion   If you disagree  you can always stick with AssertTrue for all cases

User · Answer

assertTrue will fail if the second parameter evaluates to false  in other words  it ensures that the value is true    assertFalse does the opposite   assertTrue  This will succeed    true   assertTrue  This will fail    false    assertFalse  This will succeed    false   assertFalse  This will fail    true     As with many other things  the best way to become familiar with these methods is to just experiment  -

User · Answer

assertTrue will fail if the checked value is false  and assertFalse will do the opposite  fail if the checked value is true   Another thing  your last assertEquals will very likely fail  as it will compare the  Book was already checked out  string with the output of m1 checkOut b1 p2   It needs a third parameter  the second value to check for equality

User · Answer

Your understanding is incorrect  in cases like these always consult the JavaDoc      assertFalse  public static void assertFalse java lang String message                                 boolean condition        Asserts that a condition is false  If it isn t it throws an AssertionError with the given message       Parameters          message - the identifying message for the AssertionError  null okay    condition - condition to be checked

User · Answer

The course contains a logical error       assertTrue  Book check in failed   ml checkIn b1         assertFalse  Book was aleready checked in   ml checkIn b1      In the first assert we expect the checkIn to return True  because checkin is succesful   If this would fail we would print a message like  book check in failed  Now in the second assert we expect the checkIn to fail  because the book was checked in already in the first line  So we expect a checkIn to return a False   If for some reason checkin returns a True  which we don t expect  than the message should never be  Book was already checked in   because the checkin was succesful

[java] Java/ JUnit - AssertTrue vs AssertFalse

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