De Luca, who was spending his 65th birthday before a judge, faces a possible five-year prison term in a case that has become a cause celebre for the anti-globalisation movement.
He has framed his prosecution as an assault on the right to free expression and has insisted he will go to jail rather than appeal if convicted.
He told AFP on Wednesday that he was not worried about giving evidence, despite the possibility of ending up behind bars.
"I have done so many interviews over the course of my life that I consider this hearing as just another one," he said.
At the heart of the case are statements made by De Luca in interviews in which he described as legitimate attempts to sabotage a project that has become a focus for anti-globalisation protesters.
His defence is essentially that sabotage has several possible meanings, not all of them amounting to criminal action.
"If you look in the Italian dictionary, sabotage has several meanings," he told a courtroom packed with his supporters and journalists.
"Certainly it can mean to cause significant damage, but it can also mean to stop, to disturb, to obstruct," he said in a steady and clear voice.
"I can incite (people) to read, at a push to write, but not sabotage," he said.
De Luca was prosecuted at the instigation of LTF, the Franco-Italian consortium building the multi-billion-euro link from Lyon in France to Turin in north-western Italy.
Italian authorities later joined the prosecution of the writer over the content of two 2013 interviews in which he was quoted as saying the rail link "should be sabotaged" and that he thought "it is just to sabotage it".
In court he claimed to have been misquoted on another occasion when Italian daily La Repubblica reported him as having said he had taken part in sabotage actions.
Prosecutors in the case have argued that De Luca's freedom of expression arguments are invalid since incitement to commit a crime is well-established as an example of the law placing limits on the principle.
Opponents of the rail link say it will wreck the pristine Val di Susa on the Italian side of the Alps and potentially release toxic asbestos particles into the environment.
Despite the ferocious opposition and criticism from France's public spending watchdog, the two countries' governments are strongly committed to the project, for which drilling work began in 2013.
It is expected to be completed in the late 2020s at a cost of at least €26 billion, around 40 percent of which will be provided by the European Union under a scheme to promote strategic cross-border links.
De Luca is a life-long radical whose literary tales centred on his home city of Naples have been translated into English, French, German, Spanish and a number of other languages.
He is best known for "Montedidio" (2001, translated into English as "God's Mountain" in 2002) which won one of France's best-known literary prizes, the Femina.
The next hearing in the case, where prosecutors will present their sentencing request and advocates for both sides will sum up, was scheduled for September 21st.