Homework Assignment #2 — Test Automation
In this assignment you will use tools to automatically create high-coverage test suites for different programs.
You may work with a partner for this assignment. If you do you must use the same partner for all sub-components of this assignment.
Start Early
Professors often exhort students to start assignments early. Many students wait until the night before and then complete the assignments anyway. Students thus learn to ignore "start early" suggestions. This is not that sort of suggestion.
However, once running, the tools are completely automated. Thus, you can start them running overnight, sleep and ignore them, and wake up to results. (Unfortunately, there is no way to resume an interrupted EvoSuite session without restarting it from the beginning, so be careful about laptop power and the like.)
This means that even though the assignment may not take hours of your active personal attention, you must start it days before the due date to be able to complete it in time.
Installing, Compiling and Running Legacy Code
It is your responsibility to download, compile, and run the subject programs and associated tools. Getting the code to work is part of the assignment. You can post on the forum for help and compare notes bemoaning various architectures (e.g., windows vs. mac vs. linux, etc.). Ultimately, however, it is your responsibility to read the documentation for these programs and utilities and use some elbow grease to make them work.
Subject Programs and Tools
There are two subject programs for this assignment. The programs vary in language, desired test type, and associated tooling.
PNG Graphics (C) + American Fuzzy Lop
The first subject program is libpng's pngtest program, seen earlier in Homework 1. This reuse has two advantages. First, since you are already familiar with the program, it should not take long to get started. Second, you will be able to compare the test cases produced by the black-box tool to the white-box test cases you made manually. (You'll have to recompile it with special flags, but it's the same source code.)
The associated test input generation tool is American Fuzzy Lop, version 2.52b. A mirror copy of the AFL tarball is here, but you should visit the project webpage for documentation. As the (punny? bunny?) name suggests, it is a fuzz testing tool.
You will use AFL to create a test suite of png images to exercise the pngtest program, starting from all of the png images provided with the original tarball. Note that you can terminate AFL as soon as you reach 510 paths_total (also called total paths in the GUI)— AFL does not stop on its own.
AFL claims that one of its key advantages is ease of use. Just follow along with their quick start guide. Extract the AFL tarball and run "make". Then change back to the libpng directory and re-compile libpng with a configure line like:
$ CC=/REPLACE/THIS/TEXT/WITH/YOUR/PARTICULAR/PATH/TO/afl-gcc_(don't_just_copy_this_in_unchanged) ./configure --disable-shared CFLAGS="-static"
The "CC" bit will look something like (but maybe different for you) CC=/home/vagrant/eecs481/hw2/afl-2.52b/afl-gcc — note that there is no trailing slash. If you see configure: error: C compiler cannot create executables, double-check your spelling here.
Multiple students have reported that WSL does not work with AFL and that they needed to move to an Ubuntu virtual machine instead. See the FAQ below.
Note that you are not using "coverage" or gcov for this homework assignment. I recommend re-extracting the libpng tarball into a new, separate directory just to make sure that you are not mistakenly leaving around any gcov-instrumented files. We only want AFL instrumentation for this assignment.
After that I recommend making a new subdirectory and copying pngtest and all of the test images (including those in subdirectories) to it. You can either seed AFL with all of the default images or with all of your manually-created test images (from HW1); both are full-credit options. Move those images into a further "testcase_dir" subdirectory and then run something like:
$ /REPLACE/THIS/TEXT/WITH/YOUR/path/to/afl-fuzz -i testcase_dir -o findings_dir -- /path/to/pngtest_(not_.c_nor_.png_but_the_executable_you_built) @@
Go back and double-check the end of the previous line for @@. It is required, it is not a typo, and if you did not type it in (to tell AFL where its randomly-created arguments to pngtest go) you are likely to "get stuck" when enumerating paths and tests (see FAQ below).
Note that findings_dir is a new folder you make up: afl-fuzz will puts its results there.
Note that you must stop afl-fuzz yourself, otherwise it will run forever — it does not stop on its own. Read the Report instructions below for information on the stopping condition and knowing "when you are done".
Note also that you can resume afl-fuzz if it is interrupted or stopped in the middle (you don't "lose your work"). When you try to re-run it, it will give you a helpful message like:
To resume the old session, put '-' as the input directory in the command
line ('-i -') and try again.
Just follow its directions. Warning: when you resume AFL it will
overwrite your findings/plot_data file (which you need for the
final report), so be sure to save a copy of that somewhere before resuming.
Note that afl-fuzz will likely abort the first few times you run it and ask you to change some system settings (e.g., echo core | sudo tee /proc/sys/kernel/core_pattern, echo core >/proc/sys/kernel/core_pattern etc.). For example, on Ubuntu systems it often asks twice. Just become root and execute the commands. Note that sudo may not work for some of the commands (e.g., sudo echo core >/proc/sys/kernel/core_pattern will fail because bash will do the > redirection before running sudo so you will not yet have permissions, etc.) — so just become root (e.g., sudo sh) and then execute the commands in a root shell.
The produced test cases are in the findings/queue/ directory. They will not have the .png extension (instead, they will have names like 000154,sr...pos/36,+cov), but you can rename them if you like.
Help — Can't Open AFL's Output?
You will almost certainly find that AFL's output queue folder does not contain files with the .png extension. In addition, you will almost certainly find that most of the files produced by AFL are "invalid" PNG files that cause program executions to cover error cases (e.g., libpng read error).
This is normal.
Double-check all of the instructions here, and the explanations in the course lectures for how these tools work: there's no need to panic. In addition, you might try alternate image viewers (rather than just the default one). For example, multiple students have reported that uploading apparently-invalid images to GitHub (no, really) works well for viewing them.
While AFL is running, read the technical whitepaper to learn about how it works and compare the techniques it uses to the basic theory discussed in class.
JSoup (Java) + EvoSuite
The second subject program is jsoup (v 1.11.2), a library for extracting real-world HTML data using DOM, CSS and jquery-like methods. A copy of the version of the source code known to work for this assignment is available here; you can also use git clone https://github.com/jhy/jsoup.git. It involves about 18,000 lines of code spread over 60 files. This program is a bit small for this course, but comes with a rich existing test suite. This existing test suite will serve as a baseline for comparison.
The associated test input (and oracle!) generation tool is EvoSuite, version 1.0.5. Mirror copies of evosuite-1.0.5.jar and evosuite-standalone-runtime-1.0.5.jar are available, but you should visit the project webpage for documentation.
EvoSuite generates unit tests (cf. JUnit) for Java programs.
You can install jsoup and use cobertura to assess the statement and branch coverage of its built-in test suite:
$ unzip jsoup-1.11.2.zip
$ cd jsoup-master/
$ mvn cobertura:cobertura
...
[INFO] Cobertura: Saved information on 253 classes.
Results :
Tests run: 648, Failures: 0, Errors: 0, Skipped: 11
...
[INFO] Cobertura Report generation was successful.
[INFO]
------------------------------------------------------------------------
[INFO] BUILD SUCCESS
$ firefox target/site/cobertura/index.html
Note that the supplied test suite is of high quality, with 81% line coverage and 77% branch coverage overall.
EvoSuite includes some clear tutorials explaining its use. Mirror copies of hamcrest-core-1.3.jar and junit-4.12.jar are available if you need them.
Once you have EvoSuite installed you can invoke it on jsoup via:
$ cd jsoup-master
$ $EVOSUITE -criterion branch -target target/classes/
...
* Writing JUnit test case 'ListLinks_ESTest' to evosuite-tests
* Done!
* Computation finished
You can now find the EvoSuite tests in evosuite-tests/org/jsoup. In the report you are asked to compare the coverage of the manually-created test suite to the EvoSuite-created test suite. One simple and common way to do this is by inspecting the evosuite-reports/statistics.csv file. However, you are also welcome to try integrating other coverage tools, such as clover or cobertura, with maven, but this is not required (and may be tricky).
Written Report
You must create a written PDF report reflecting on your experiences with automatic test generation. You must include your name and UM email id (as well as your partner's name and email id, if applicable). In particular:
- In a few sentences, your report should describe one test case that
AFL created that covered part of libpng that your manual test
suite from Homework 1 did not, and vice versa. (If no such tests exist,
for example because you seeded AFL with all of your manual tests, instead
describe what did happen. For example, if you seeded AFL with all of your
manual tests, then AFL's output will be a superset of yours.) You should
also indicate how many tests your run of AFL created, your total runtime,
and the final coverage of the AFL-created test suite (use the technique
described in Homework 1 to compute coverage; note that AFL will include
all of the original tests as well — yes, you should include those).
[2 points for AFL, 2 points for manual, 1 point for summary] - Your report should include, as inlined images, one or two
"interesting" valid PNG files that AFL
created and a one-sentence explanation of why they are "interesting".
[1 point for image(s), 1 point for explanation] - Your report should include a scatterplot in which the x axis
is "seconds" (or some other notion of total execution time, such as
unix_time) and the
y axis is paths_total as reported in
the findings/plot_data CSV file produced by your run of AFL. You
can create this plot yourself (using the program of your choice, or even
the now-familiar jfreechart!). Your scatterplot must include
data reaching at least 510 paths_total on the y axis
— which means you must run AFL until you have at least that much
data. (See here for plot examples
that include much more detail than you are asked to include here. Note
that this is not own finds but is instead total
paths in the upper right corner.
Include a sentence that draws a conclusion from this scatterplot. If you
do not like scatterplots you can make a line graph (etc.) as long as it
conveys the same information.
Note that it does not matter how many rows are in your plot_data file or if you are missing some rows at the start or middle as long as you got up to 510 paths_total (also called paths total in the GUI)— it is common to have fewer than 510 rows.
Note that if you suspended afl-fuzz you may have a big time gap in your plot. We do not care how you handle that (e.g., ugly graph, big gap, fudge the times, whatever) — any approach is full credit.
[2 points for plot, 1 point for conclusion] - Look at evosuite-report/statistics.csv and compare it to
target/site/cobertura/index.html. In a few sentences, compare
and contrast the branch coverage of the manually-created test suite to
the EvoSuite-created test suite.
[2 points for a comparison that does more than just list numbers] - Choose one class for which EvoSuite produced
higher coverage than the human tests (if no such class exists, choose
EvoSuite's "best" class). Look at the corresponding tests.
(You will have to look carefully at the automatically- and
manually-generated tests to answer this question.)
In
one paragraph, indicate the class and explain the discrepancy. For
example, in your own words, what is EvoSuite testing that the
humans did not? Why is EvoSuite more likely to generate such
a test? What do you think of the quality of the tests? The readability?
Suppose a test failed. Would the test's failure help you find the bug?
[4 points for a convincing analysis that shows actual insight] - Choose one class for which EvoSuite produced lower coverage
than the human tests (if no such class exists, choose EvoSuite's
"worst" class). Elaborate and reflect as above, but also offer a
hypothesis for why EvoSuite was unable to produce such a test: bring
in your knowledge of how EvoSuite works.
[4 points for an analysis that shows insight, especially into EvoSuite's limitations] - In one paragraph, your report should compare and contrast your
observations (e.g., usability, efficacy, test quality) of AFL and
EvoSuite. List at least one strength of each tool and at least
one area for improvement. Which software engineering projects might
benefit from the use of such tools? Would you use them personally? Why or
why not?
[1 point for AFL strengths and weaknesses, 1 point for EvoSuite strengths and weaknesses, 3 points for insightful analysis]
This does not have to be a formal report; you need only answer the questions in the rubric. However, nothing bad happens if you include extra formality (e.g., sections, topic sentences, etc.).
There is no explicit format (e.g., for headings or citations) required. For example, you may either use an essay structure or a point-by-point list of question answers.
The grading staff will select a small number of excerpts from particularly high-quality or instructive reports and share them with the class. If your report is selected you will receive extra credit.
Submission
For this assignment the written report is the primary artifact. There are no programmatic artifacts to submit (however, you will need to run the tools to create the required information for the report). (If you are working with a partner, you must select your partner on Brightspace and submit one copy of the report. However, nothing fatal happens if you mistakenly submit two copies.)
Commentary
This assignment is perhaps a bit different than the usual EECS homework: instead of you, yourself, doing the "main activity" (i.e., creating test suites), you are asked to invoke tools that carry out that activity for you. This sort of automation (from testing to refactoring to documentation, etc.) is indicative of modern industrial software engineering.
Asking you to submit the generated tests is, in some sense, uninteresting (e.g., we could rerun the tool on the grading server if we just wanted tool-generated tests). Instead, you are asked to write a report that includes information and components that you will only have if you used the tools to generate the tests. Writing reports (e.g., for consumption by your manager or team) is also a common activity in modern industrial software engineering.
FAQ and Troubleshooting
In this section we detail previous student issues and resolutions:
-
Question: Using AFL, I get:
ERROR: PROGRAM ABORT : Test case 'xxxxxx/pngtest' is too big (2.25 MB, limit is 1.00 MB)
Answer: You are mistakenly passing the pngtest executable in as a testcase to itself. Try putting your pngtest executable one directory above from your testcase_dir. In other words, rather than having it in the same folder as your test images (testcase_dir), put it in the directory that testcase_dir is in, and adjust /path/to/pngtest accordingly.
-
Question: My AFL session has 0 cycles done but the total paths counter does increment. I am worried.
Answer: Everything is fine. It is entirely possible to complete the assignment with 0 cycles done. (AFL can enumerate quite a few candidate test cases — enough for this assignment — before doing a complete cycle.)
-
Question: My ssh sessions keep getting disconnected. How can I avoid losing my work from a long-running job?
Answer: Two common approaches are to use the nohup command or the screen command. There are a number of helpful tutorials online to get you started.
-
Question: Using AFL, I get:
[-] SYSTEM ERROR : Unable to create './findings_dir/queue/id:000000,orig:pngbar.png'
Answer: This is apparently a WSL issue, but students running Linux who ran into it were able to fix things by making a new, fresh VM.
-
Question: Using AFL, I get:
[-] PROGRAM ABORT : Program 'pngtest' not found or not executable
or[-] PROGRAM ABORT : Program 'pngnow.png' is not an ELF binary
Answer: You need to use the right /path/to/pngtest instead of just pngtest. You must point to the pngtest executable (produced by "make") and not, for example, pngtest.png.
-
Question: Using AFL, I get:
[-] PROGRAM ABORT: Program 'pngtest' is a shell script
Answer: You must recompile libpng carefully following the instructions above, including the explanation about "CC=..." and "--disable-shared" and the like. Example showing that a normal build produces a shell script while a more careful AFL-based build produces an executable:
$ ./configure >& /dev/null ; make clean >& /dev/null ; make >& /dev/null ; file ./pngtest ./pngtest: Bourne-Again shell script, ASCII text executable $ CC=~/481/afl-2.52b/afl-gcc ./configure --disable-shared CFLAGS="-static" >& /dev/null ; make clean >& /dev/null ; make >& /dev/null ; file ./pngtest ./pngtest: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/l, for GNU/Linux 3.2.0, BuildID[sha1]=bec3dc8e4b3feff6660f9339368f5c1ec5f55ab9, with debug_info, not stripped
Question: When I try to run AFL, I get:
[-] PROGRAM ABORT : No instrumentation detected
Answer: You are pointing AFL to the wrong pngtest executable. Double-check the instructions near $ CC=/path/to/afl-gcc ./configure --disable-shared CFLAGS="-static" , rebuild pngtest using "make", and then point to exactly that executable and not a different one.
Question: When I try to run configure with AFL via something like CC=/home/vagrant/eecs481/p2/afl-2.52b/afl-gcc/ ./configure --disable-shared CFLAGS="-static" , I get:
checking whether the C compiler works... no configure: error: in `/home/vagrant/eecs481/p2/libpng-1.6.34': configure: error: C compiler cannot create executables
Answer: You need to specify afl-gcc, not afl-gcc.c or afl-gcc/ (note trailing slash!).
Question: When I am running AFL, it gets "stuck" at 163 (or 72, or another small number) paths.
Answer: In multiple instances, students had forgotten the @@ at the end of the AFL command. Double check the command you are running!
Question: When trying to use AFL on Amazon EC2, I get:
[ec2-user@ip-172-31-19-147 afl-2.52b]$ make [*] Checking for the ability to compile x86 code... /bin/sh: cc: command not found Oops, looks like your compiler can't generate x86 code.
Answer: One student reported resolving this via sudo yum groupinstall "Development Tools".
Question: When I try to compile libpng with AFL, I get:
configure: error: C compiler cannot create executables
Answer: You need to provide the full path to the afl-gcc executable, not just the path to hw2/afl-2.52b/.
Question: Some of the so-called "png" files that AFL produces cannot be opened by my image viewer and may not even be valid "png" files at all!
Answer: Yes, you are correct. (Thought question: why are invalid inputs sometimes good test cases for branch coverage?)
Question: Cobertura suggests that the project has 3,726 branches, but EvoSuite seems to think they sum up to 5,149. What gives?
Answer: Good observation! Everything is fine. Double check the lecture slides. What are some ways in which two tools could disagree about the number of "branches" in the same Java classes?
Question: When trying to run EvoSuite, I get:
-criterion: command not found
Answer: This almost always indicates some sort of typo in your export EVOSUITE=... setup line.
Question: Can I terminatie EvoSuite and resume it later?
Answer: Unfortunately, no. I emailed the author who indicated that this is not currenltly possible.
Question: What does "interesting" mean for the report? Similarly, how should we "elaborate" or "reflect"?
Answer: We sympathize with students who are concerned that their grades may not reflect their mastery of the material. Being conscientious is a good trait for CS in general and SE in particular. However, this is not a calculus class. Software engineering involves judgment calls. I am not asking you to compute the derivatives of various polynomials (for which there is one known right answer). You are carrying out activities that are indicative of SE practices.
Suppose you are tasked with evaluating a test generation tool for your company. You are asked to do a pilot study evaluating such a tool and prepare a report for your boss. One of the things the boss wants to know is: "What are the risks associated with using such a tool?" Similarly for the benefits or rewards.
Question: Can I use free cloud computing, like Amazon EC2, for this assignment?
Answer: Sure. Here's what one student had to say:
If you can get over the hump of setting up AWS (pro-tip they have lots of documentation, use google. also here you go), their free-tier EC2 instances can get the AFL job done in a blink. Using their free-tier EC2 Ubuntu instance, I was able to run AFL up to >500 paths in 5 minutes. Setup would probably take less than 30 minutes for a new user. IMO that more than balances the headache of having to run AFL for hours and hours and hours and hours.
Question: I am using WSL, and when I try to run AFL I get:
$ CC=/mnt/c/users/.../481/hw2/afl-2.52b/afl-gcc ./configure --disable-shared CFLAGS="static" checking for a BSD-compatible install... /usr/bin/install: setting permissions for '/mnt/c/users/.../hw2/libpng-1.6.34/conftest.dir/conftest.one': Operation not permitted ... configure: error: in `/mnt/c/users/.../481/hw2/libpng-1.6.34': configure: error: C compiler cannot create executables
Answer: Students were able to resolve this by not using WSL and instead using an Ubuntu virtual machine.
Question: How can I make AFL run faster?
Answer: One anonymous student suggests:
Is your AFL running slow? Are you getting less than 30/sec on the exec speed? Have you been running for 21+ hours like me and are frustrated that you haven't found any new paths in the last 4 hours?Try making a copy of your test image directory, then remove any "large" test images from this new directory (I deleted all test images over 100KB), and then try running a new AFL session with this new input directory, and a new output directory. Each "session" of AFL basically runs in a single thread, so it seems to be fine running two different sessions at once, with different input/output directories. I watched as my new run (with small test image files) consistently ran with an exec speed of 500-1000, and achieved 600 total paths in under 7 minutes, all while safely letting my old session continue to run.
tl;dr Don't use lots of "large" images with AFL (large roughly being >100KB)