Please keep it to the topic. I feel like you are evading some of my points.
1. Well by allies I mean that countries supported by a more powerful nation, by both financial and military means. In many cases, weaker countries allow the stronger ally to carry military operations on their territories. The China-US relationship was what I call "political friendship", ready to backstab each other given the opportunity and benefit. Prior to the border war, Vietnam-China was considered allies. Think about it, China supported Khmer Rogue just like it used to support Vietnam.
2. No, I personally do not blame China for that. China acted in the interest of herself, Vietnam acted for hers. Our interests conflicted and they became hotter and hotter. No one came in to defuse it in time so war happened.
Why did China need a test war? Maybe to prepare for what is happening right now. It's just 35 years, you know.
3. I have no comment for you. Stopping genocide was not good enough for Cambodia, then what could be better?
4. The US even used their fighter to keep Vietnam bomber out of the border. Why did they let our land force enter Thailand? And where is the Thai army? For the record, there is no clash between Thai and Viet forces during that time. Do you have any sources?
5. The CCCP and most of the communist block were in the middle of a total crisis, both financial and political at that time. Could they care to errect more communist gov if they could not maintain their own?
6. Every coin has 2 sides, same goes to stories. I am a young generation who has not experience wars so I am not in the position to judge.
I don't know about your side of story but Vietnam gov under Uncle Ho is afraid of "blood debt" (letting foreigners fight and die for Vietnam). You know when the WWII ended, China (the ROC gov) used to send 20,000 troops to disarm Japanese troops in North Vietnam, why France took care of South Vietnam. Did you think Chiang Kai-shek did not want to establish a puppet gov to support him? I believe he used to "suggest" to aid Vietnam chasing the French out in exchange for the control of the Parliment. Vietnam refused because they knew the Parliment was not enough to pay back the blood of Chinese troops fought for Vietnam, in fact nothing is enough. Back to the topic, in Vietnam-US war, both CCCP and China also made the same suggestion, because at that time they were officially allies to Vietnam. Yet Vietnam still refused. Vietnam accepted both countries to send engineers, military advisors and trainers, with a small force to protect them (just like the US did during the beginning of the war). Vietnam did not allow them to fight in the frontline. The majority of KIAs of Chinese and Soviet troops were mostly due to the bombing of North Vietnam carried out by the US. Vietnamese are in debt to those soldiers, and we pay respect to them. But to their gov, urgh, not so much.
"There is no eternal friendship, only eternal benefit", that's what I read from a Chinese book. When Vietnam-China were at war, each side tried their best to make it look good while the other look bad. Your gov might say China supported everything for Vietnam then Vietnam betrayed China. My gov said that China stole a lot of Soviet supplies to Vietnam and then stamped its seal on the rest, claimed it their supplies and Vietnam was in debt for that. We each trusted our gov and blame the other. But you and me must understand that, gov is gov, and people are people. We cannot hate the people for what their gov does. Have an open mind and hear the story from the other side. Then judge it to yourself.