SoCraTes Day: Testing the Impossible

21. June, 2015

I’m back from SoCraTes Day Switzerland where I help a Code&Hack session called “Testing the Impossible”.

The session is based on this Mercurial repository de.pdark.testing.


  • 20150619_105103-socrates-day-testing-the-impossible-page1Space Shuttle – They Write the Right Stuff
    • Why wasn’t the bug caught by QA?
    • Why did the bug escape dev?
  • Personal Bug Diary
  • Team Culture: Strengths va. Blame Game
  • Miscommunication with Customers
  • Anyone can press the “Red Button
  • Make failures cheap. Fail fast.
  • I’m wrong. I have learned something.
  • Bug-.hunting takes time and mindshare.
  • If you found a bug, write a test for it

How do I test randomness?

  1. Test small pieces
  2. Fix things that varies (IDs, timestamps, etc.)

How do I test a DB?

  • 20150619_105103-socrates-day-testing-the-impossible-page2Layer between DB and App code which allows to switch between real DB and mock
  • Verify generated SQL instead of executing it
    • Fast
    • Allows to test thousands of combinations easily
    • Useful for code that builds search queries
  • Run SQL against real DB during the night (CI server)
  • H2 embedded DB can emulate Oracle, MySQL, PostgreSQL, …
  • Test at various depths (speed vs. accuracy)
  • Testing Walrus dives deep!

Getting Started with Onshape: Sketches

13. April, 2015

This is the first part of a series of posts about Onshape. In case you don’t know, Onshape is a cloud-based, online parametric CAD. The result of the tutorial is in this document.

After signing up, you’ll find yourself in the documents page:

Document Page

Click “Create” to create a new one. I’d like to design an office chair, so I’ll use “Office Chair” as document name.

Onshape will now display the workbench:

Onshape Workbench

Read “Interface Basics” to learn how to manipulate the UI. I’d like to get started with my chair. The first thing that it needs is wheels.

Let’s create a circle … circle … where is the circle? Where is anything???

Turns out that Onshape wants to you to create a “sketch” first. Think of a sketch as an outline of something. With the tools that you can see now, you can turn this outline into a 3D object. Sounds a bit dry but wait for it. To create a sketch, click on the “Sketch” button (next to the pencil).

New Sketch

There are three important points here:

  1. Onshape tells us what we need to do next.
  2. The new sketch was added to the features.
  3. Blue things are important or active. In this case, the “Sketch Plane” selector is active and Onshape wants us to select a plane. If it turns grey, make sure you click it again or the next step won’t work.

What does that “a sketch plane” mean? Onshape is a 3D CAD but you probably only have a 2D mouse. That means Onshape somehow has to reduce one dimension. It does that by letting you select a plane on which all your lines, rectangles and circles will be. We’ll see how that works out later when we create more complex shapes.

Currently, we want to create a wheel and a wheel should stand on the floor (or it won’t move). So we have the choice of the “Front” and the “Right” plane. I chose the “Front” plane. Just move the mouse over the plane you want and it should turn yellow. If you click, the “selection” will be added to the sketch:

Selected Front plane

As you can see, the blue field turned white, the text changed to “Front plane” and there is now an additional rectangle in the 3D view. If you rotate the view, you’ll see that the new rectangle is always parallel to the “Front” rectangle which is what we want.

Also the missing primitive drawing tools (line, rectangle, circle) are now available.

Let’s build a wheel. Let’s start with a circle. Click the green button and … Where did the drawing tools go??? Where is my sketch? What is going on?

Well, the drawing tools are only visible as long as you’re editing a sketch. So double-click on “Sketch 1″ or right-click it and select “Edit”. And the tools are back.

Let’s add a circle:

  1. Click the Circle button at the top (it turns grey to indicate that it’s now active)
  2. Click somewhere in the drawing area and drag the circle as big as you want.

I had my first doubt here: How do I enter a diameter or radius? How am I supposed to construct something instead of simply sketching a design? Turns out that Onshape has solved this problem in a really nice and intuitive way. But let’s assume that we have no idea and we just continue working.

If you rotate the view, then the planes “Front”, “Sketch 1″ and the circle should look like they are parallel.

We now have the outline of our wheel. The sketch is now ready to be used. Finish editing by clicking the green button.Added circle

Your workspace should now look like this: “Sketch 1″ in the list of features and a dull grey circle. Let’s turn the circle into a cylinder. Click “Extrude” (first button to the right of sketch).


Important things here: The extrude operation has been added after the sketch. That means it can use our sketch as outline for the operation.

The options for extrude are what we want (“Solid” and “New”). The next option (active) is the outline to extrude. Hover inside the circle and it will turn yellow. When you click, the magic will happen.

Extrude At Work

If you drag the arrow around, you can see that the number in the Extrude form changes. That’s the amount by which the outline gets extruded. You can also edit the value directly. Enter “1 cm”. The software will display “0.394 in” and update the cylinder. If you edit the value, you’ll see “1 cm” again. So the software remembers what you originally wanted. Keep that in mind.

Most wheels have round edges. The “Fillet” tool does that for us. Click on the tool without closing the “Extrude 1″ form:

Wheel Fillet

As you can see, the last tool was finished for us and a new one was added. “Fillet 1″ is waiting for us to select the corners we want to round. If you hover over the two ends of the cylinder, they’ll turn yellow (as in the image above). When they do, click to add them. There is no need for Ctrl or Shift, Onshape always toggles the selection when you click on something.

You’ll notice something strange: When you select the first circle, the edge will be rounded. But when you select the second one, the effect will be gone. Why?

Odd Fillet Behavior

In the form, you can see that the correct edges are selected. The problem is that the radius of the fillet (0.2 in) is too big; 0.4 in is greater than 1 cm, so Onshape simply can’t do what we want. Enter “3 mm” to fix that:

Finished First Wheel

Looks like a wheel to me. But “0.118 in” looks odd. Let’s fix that. Onshape Units

Select “Centimeters”. The form won’t update right away, you have to close and reopen it.

Let’s add an axis around which the wheel should rotate. Create a new sketch (“Sketch 2″). Select the side of the wheel as “sketch plane” which is closest to the plane of “Sketch 1″.

Add a circle. This time, hover the mouse near the center of the wheel until the center point lights up. That tells Onshape that you want a circle which has the same center as the first one:

Wheel Axis Center

The important part here is the little icon with the two lines and the white point. This is a constraint, specifically the “Coincident constraint” which makes sure that those two points will stay in the same place, even when you move one. This will start to make sense later.

After adding the circle, we want to make sure it’s exactly 1 cm. How do we do that?

With the dimension tool. Click it and the circle. You’ll get an entry field where you can enter “1 cm” to set the diameter of the circle:

Wheel Axis Dimension

Click extrude to add a 0.6 mm long cylinder. You need to click inside of the new circle to make this happen:

Extruded Wheel Axis

Important bits here:

  1. The option “Solid” is active.
  2. The option “Add” is active. This adds the new volume to the part selected at the bottom (“Part 1″)
  3. “Face of Sketch 2″ is selected which is our circle. That’s the outline that gets extruded.

To create the second wheel, we add a mirror operation. Click “Mirror”, select the wheel somewhere. It will turn yellow-ish:

Wheel Mirror, Step 1

The field “Mirror plane” is red, indicating some kind of problem. Note that the field with “Part 1″ is active, so click anything would change this field. We don’t want that. Click on the field “Mirror plane,” instead. You should now be able to select the top of the axis:

Selecting Mirror Plane


which will give you this result:

Two Wheels with Axis


Two wheels, connected with an axis.

How big are the wheels? If you remember, we just dragged a circle. Dimension tool to the rescue!

Double click “Sketch 1″ to edit it. Everything else will be hidden.

Apply the dimension tool to the circle. Enter “6 cm”. Click the green button to get:

Two Wheels with Correct Size

And that’s the power of Onshape: The tool remembers all the steps that you made to create something. If you go back and change a step, it will adjust all the later steps. That means you can really “sketch” (as in “quickly draw something”). When you feel the need to improve a step, go back to it, make the change and everything else will be updated.

As the last part of this tutorial, let’s add the handle which connects the axis between the wheels and the base of the chair.

I’ll construct a simple handle from a box and a cylinder. For the box, I first need a rectangle which goes between the wheels.

While I could rotate the view carefully and aim between the wheels, there is a more simple way: Hide the second wheel for a moment. To do this, right-click on “Mirror 1″ and select “Suppress” from the context menu:

Hiding the Second Wheel

We can now easily create a sketch in the same plane as the extruded tip of the axis. Draw a rectangle around the axis which should extend somewhat to the left side of the wheel without extending over the wheel itself:

Rectangle Outline of the Handle

Extrude it. Options: “Solid”, “New”, Change “Blind” to “Symmetric”, “0.8 cm” thick, and make sure you click on the area of the rectangle outside of the circle which marks the axis. That way, we get a hole in the new box for free:

Extrude Box With Hole

If you don’t get a hole, remove the selection of “Face of Sketch 3″ with the little red “x” next to it (not the big one at the top!) and click again.

Time for the last sketch: The cylinder at the top.

  1. Click “Sketch”
  2. Select the top of the new box
  3. Switch to “Top” view
  4. Draw a circle

Messy Circle

But we want the circle to be perfectly aligned. For that, we need construction lines.

  1. Delete the circle again (try Undo)
  2. Create a vertical line near the right end of the box. Make sure the “coincident” symbol is visible when you click. When you click a second time, you should also see the “perpendicular” symbol.
  3. Select the vertical line
  4. Click the “Construction” tool to turn it into a dashed construction line
  5. Click the “Dimension” tool
  6. Select the vertical line and the right edge of the box.
  7. Enter “0.4 cm” as distance
  8. Create a circle with the center point at the midpoint construction line
  9. Use the dimension tool to give the circle a diameter of 6 mm

The final result should look like this:

Constructed Circle

Finally, extrude the circle by 2.5 cm:

Hollow Tube

This doesn’t look right. In the “Extrude” form, “Surface” is selected but we need “Solid.”

Missing Cylinder

What the …? Where is my cylinder??

Turns out that it makes a difference what you select before you extrude. If you select the circle outline, you get only a tube. But if you click inside of the circle, the whole area is extruded. So to fix the problem, just click inside of the circle (instead of the circle itself) to get:

Correct Cylinder

Make sure “Add” is selected and “Part 2″.

Last steps:

  1. Unsuppress “Mirror 1″
  2. Rename the tab from “Part Studio 1″” to “Wheel Parts”

Finished Wheels

Not bad for just a few minutes of work. Next part: Chair Base with 5 spokes.

TNBT: Proactive IDEs

13. February, 2015

Imagine this situation: You’re working on some code and you get an exception when you run the unit tests. Next to the output is a link with the text: “User Joe had the same exception two months ago and fixed it with the commit b8cfda02.”

How would that work? We’re using big data for all kinds of things, tracking customer happiness, searching the Internet and discovering terrorist threats (or not).

Standard development teams have about 10 people. That means you have a super computer with 40-80 cores, 160 GB of RAM and 20 TB of disk space connected with a fast LAN in your office already. That beast is usually idling while it waits for the developers to press keys. It would be pretty simple to install a clustered log analyzer on this hardware which simply reads all the log files and reports which Maven and running JUnit test creates. It would be as simple to connect the same database to your version control. That means this system could track all the errors and exceptions that you get when you run unit tests or the whole application.

This information could then be used to detect when someone in the team gets a new exception plus the change sets which fixes them. If the system detects an exception which it has seen before, it can tell you which developer has fixed it or who is currently working on it – instead of wasting your time, you could see the code which contains the solution or ask someone who has already solved the problem.

With proper filtering, the data could be split into internal and framework code. That way, the system could report to library projects where consumers struggle most.

On the large scale of things, this system can tell you which parts of the system are most brittle.

As usual with big data, there are some downsides. The same system would tell you which developer breaks the code most often. Who writes the worst code. If your manager isn’t able to see the human value in his charges, this might not be your best bet.

Related Articles:

  • The Next Best Thing – Series in my blog where I dream about the future of software development

Hibernating openSUSE 13.2 (Harlequin)

8. February, 2015

openSUSE 13.2

I had some trouble to get hibernate (suspend to disk with power off) to work properly on openSUSE 13.2. You can find the problems that I ran into and how I solved them below.

Getting a Boot Menu

Since a while, Linux systems try to hide the fact that they’re Linux. You switch the PC on and after a few seconds, you see a desktop. I hate that. So the first step is to get the boot menu back. Edit /etc/default/grub and look for GRUB_TIMEOUT. It’s 0 now, set it 8:


Note: You can’t use YaST for this. YaST can only modify GRUB_HIDDEN_TIMEOUT which is not very useful IMO.

After making these changes, run grub2-mkconfig as explained at the top of /etc/default/grub to update Grub 2’s configuration.

See also: GRUB Manual 2.00: Simple configuration

Authorize Hibernate

If you tend to get this dialog when you try to hibernate:

Legitimierung ist zum Aktivieren des Ruhezustands des Systems notwendig, während andere Benutzer angemeldet sind. – PolicyKit1-KDE_016

then someone else is logged in. In my case, I sometimes have a root shell lying around somewhere or an SSH session. There are two solutions to this problem:

  1. Hibernate. Wait. Realize that the system won’t hibernate. Log in again. Find the error dialog. Close it. Find the root shell. Log out root. Try again. Don’t forget to mumble curses all the time since it’s 2:00am and you want to go to bed instead of fighting a security policy.
  2. Tell polkit that if the user in front of the display wants to hibernate, then simply do it!

To do the second, edit the file /etc/polkit-default-privs.local and append this line:

org.freedesktop.login1.hibernate-multiple-sessions auth_self:auth_self:yes

After making the change, you need to run /sbin/set_polkit_default_privs to activate the changes; no reboot or relog necessary.

The first word in the line is the operation, the second one is the permissions. The default for *.hibernate-multiple-sessions is auth_admin:auth_admin:yes which means “ask for root privileges” which makes sense for a server or a shared PC where people connect remotely. auth_self means “Authentication by the owner of the session that the client originates from is required” which should be good enough for any standalone/private PC.

Related: Polkit man page

Hibernate KDE With a Single Click

Something that I’m missing since a long time is a way to hibernate a KDE desktop at the push of a button. Options from worst to best:

  1. Open the start menu. Try to navigate to the shutdown options without accidentally closing the menu. Wonder which of the options is the right one for the millionth time. Click and hope for the best.
  2. Open a root shell, keep it open at all times and run the command /usr/sbin/pm-hibernate
  3. Use KShutdown
  4. Allow yourself to execute the command /usr/sbin/pm-hibernate via sudo without asking for a password. Put sudo /usr/sbin/pm-hibernate into a script and wrap the script with an icon on the desktop.
  5. Issue the hibernate command via shell script and wrap the script with an icon on the desktop.

Options #1 is too cumbersome. #2 wastes too many resources. #3 isn’t standard and I’ve found it increasingly difficult to find the binary for my system. #4 doesn’t lock your screen so anyone able to turn on your computer can mess with it.

So here is how to do #5. First, we need a shell script$HOME/bin/hibernate with this content:

dbus-send \
  --session \
  --dest=org.freedesktop.PowerManagement \
  --type=method_call \
  /org/freedesktop/PowerManagement org.freedesktop.PowerManagement.Hibernate

How let’s create a button for the script:

  1. Make the script executable with chmod +x $HOME/bin/hibernate
  2. Right click on the desktop, add applet “Folder View” (German: “Ordner”).
  3. Create a new folder $HOME/Hibernate and select this new folder in the settings. That gives you a small window on the desktop that you can size and move – perfect to position our button.
  4. Right click in the new window and create a shortcut for a program.
  5. Enter “Hibernate” as name on the first tab.
  6. On the program tab, select the script.
  7. Click OK.
  8. Open the properties for the new shortcut.
  9. Click the icon to replace it.
  10. In the new dialog, select “Actions” and search for “hib” which should offer you “system-suspend-hibernate” Click the icon to select it.
  11. Click OK
  12. Size and move the folder view to have the button where you want it.

Eclipse is Slow – Finding out Why

8. January, 2015

In this article, I’m trying to collect the steps to find out the reason when Eclipse is suddenly slow:

  1. Java GC. To find out if that’s the culprit, go to Window -> Preferences -> General and enable “Show heap status”. You will get a little gauge at the bottom of the Window. If the gauge is almost full, then you probably have too little memory.
    a) Give Eclipse more memory
    b) Close some projects
    c) Deinstall or disable unnecessary plugins
  2. Check the Eclipse Error Log. Maybe there is a problem under the hood.
  3. Some plugin is acting up. Enable Eclipse’s own logging (see below) and watch the console.
    Some plugins have their own console (Groovy, Maven). In the Console View, click the arrow of the “Open Console” button to get a list. The Stacktrace Console – a useful tool to examine stacktraces from some external source – is also hidden there.
  4. The metadata got corrupted. Clean it.

Enable Eclipse’s Console Logging

When you start a Java application inside of Eclipse, you can see the output in a console view. You can do the same for Eclipse itself.

Open eclipse.ini and add these lines right before -vm (or -vmargs, if there is no -vm line):


See “Debug Mode“, “Eclipse runtime options” and “FAQ How do I use the platform debug tracing facility

On Windows, make sure Eclipse is started with java.exe instead of javaw.exe.

Eclipse will log errors and trace information to the console window. Check the output.

Enable Tracing

Many Eclipse plugins offer a range of trace options. You can see them if you open the plugin JARs. Look for a file called “.options”.

If you copy some of those into a file “.options” in the same folder as “eclipse.ini”, you can able various logging options.

Here is an example what the file could look like:


Maven m2e Plugin

If the m2e plugin causes problems:

  1. Look into the Maven console.
  2. Try Maven from the command line to see whether it’s a problem with the project in general or with m2e.
  3. Tweak the logging options of m2e by editing

m2e FAQ

App to Manage Terms and Conditions

28. December, 2014

There is this old joke on User Friendly about license agreements: “Have any of you ever actually read a license agreement?” “I have! A few words, anyway …” “And what did the part you read say?” “umm… ‘I accept.'” (whole story starts here; afterwards, someone actually wrote a version of Clippy for Vim called Vigor).

I remembered all this when I saw this video on YouTube:

And that led me to an idea: How about an app which tracks T&C for you? In general, it should take a license and show you the important bits. Then, you could say “okay, I like that and that and I can live with those.” The app would then remember your preferences. For the rest of the terms, you could chose “I grudgingly accept these” or “no business with me because of this term.”

Even better, the app could notify you of terms which don’t apply to you because of local law or because courts ruled them out.

That way, the app could just show you the parts of a new license which you want to know about, that is the parts which you didn’t already agree to and without the parts that you’d accept anyway.

c’t Inhaltsverzeichnis sortieren

23. December, 2014

Eine kleine Hilfe für alle Leser der c’t, welche einfach(er) einige Artikel archivieren wollen: Das verlinkte Script unten sortiert das Inhaltsverzeichnis im Archiv nach Seitenzahl wenn man auf “aktuell” klickt.


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