POM: Check explicitly for /opt/local/bin/dot

Currently when running mvn clean install in the root directory of the project, I get something like this:

Tests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.241 sec - in org.sahli.asciidoc.confluence.publisher.converter.FolderBasedAsciidocPagesStructureProviderTest
Running org.sahli.asciidoc.confluence.publisher.converter.AsciidocConfluenceConverterTest
java.io.IOException: Cannot run program "/opt/local/bin/dot": error=2, No such file or directory
	at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
	at java.lang.Runtime.exec(Runtime.java:620)
	at net.sourceforge.plantuml.cucadiagram.dot.ProcessRunner$MainThread.startThreads(ProcessRunner.java:158)
	at net.sourceforge.plantuml.cucadiagram.dot.ProcessRunner$MainThread.runJob(ProcessRunner.java:118)
	at net.sourceforge.plantuml.api.TimeoutExecutor$MyThread.run(TimeoutExecutor.java:74)
Caused by: java.io.IOException: error=2, No such file or directory
	at java.lang.UNIXProcess.forkAndExec(Native Method)
	at java.lang.UNIXProcess.<init>(UNIXProcess.java:247)
	at java.lang.ProcessImpl.start(ProcessImpl.java:134)
	at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
	... 4 more
java.io.IOException: Cannot run program "/opt/local/bin/dot": error=2, No such file or directory
	at java.lang.ProcessBuilder.start(ProcessBuilder.java:1048)
	at java.lang.Runtime.exec(Runtime.java:620)
	at net.sourceforge.plantuml.cucadiagram.dot.ProcessRunner$MainThread.startThreads(ProcessRunner.java:158)
	at net.sourceforge.plantuml.cucadiagram.dot.ProcessRunner$MainThread.runJob(ProcessRunner.java:118)
	at net.sourceforge.plantuml.api.TimeoutExecutor$MyThread.run(TimeoutExecutor.java:74)
Caused by: java.io.IOException: error=2, No such file or directory
	at java.lang.UNIXProcess.forkAndExec(Native Method)
	at java.lang.UNIXProcess.<init>(UNIXProcess.java:247)
	at java.lang.ProcessImpl.start(ProcessImpl.java:134)
	at java.lang.ProcessBuilder.start(ProcessBuilder.java:1029)
	... 4 more

Suggestion: Check for the existence of that tool explicitly in the POM, and fail fast when it does not exist, explaining why the tool is needed, and suggest how to install it.

E.g. on macOS, the instruction could be:

• install Homebrew
• brew install graphviz

[Aloren]

When I started working with the project – that was the same issue I’ve faced 😄 I suppose (since this such a common issue), that the tests instead of failing with Cannot run program "/opt/local/bin/dot" should be failing with something more descriptive like “Please install GraphViz package to run these tests. See more info at: link to contributing guide”.

[cstettler]

Hi @znerd, as I see your point (but was not very happy with the pom-based approach with the hardcoded path), I tried another approach using a JUnit class rule based on the actual PlantUML lookup mechanism. It is available on branch feature/graphviz-installation-check and should be on master soon.

The main issue I see with not doing anything for this issue is that the tests fail, but only due to different image dimensions as PlantUML is rendering the error message as an image (maybe not exactly the type of error handling we would expect …).

I was also checking for a way to actually detect the issue when converting the Asciidoc content (that would help during production usage, too), but so far was not able to find a hook to get into the PlantUML conversion process through JRuby.