The Soviets were the first country to put a man in orbit, a woman in orbit, and a black man in orbit. They were not being progressive for progress's sake, but it wouldn't be fair to describe these cosmonauts as test dummies. These three "firsts" were all accomplished for propaganda and publicity reasons.

The first woman in space, Valentina Tereshkova, was chosen for her skydiving ability. Like Yuri Gagarin two years earlier, she was crammed into a tiny uncomfortable capsule and launched into orbit, where she communicated by radio, took photos, and made measurements. This was another win in the Space Race against America, and many Soviet newspapers kept score. The first orbit, the first animal in space, first man in space, and now the first woman. The Soviet Union was very conscious of the publicity surrounding the Space Race, and wanted to ensure they were the first to get a woman in orbit. Launching a woman into space didn't require any new technology, but it was a propaganda coup for the Soviets.

17 years later the first black man in space, Arnaldo Mendez, had a longer and more technical flight than either Tereshkova or Gagarin. He was a former fighter pilot, and he spent seven days aboard the Salyut space station, where he conducted experiments on preventing space sickness and on crystal formation. Although space was less relevant in the public conscious in 1980, some Soviet newspapers used Mendez's achievement as a contrast against racism in the United States. It was also helpful in maintaining Cuban-Soviet relations. I haven't seen anything to suggest that his mission was particularly dangerous or unpleasant.

I wrote an answer about lost cosmonauts and test dummies here. The long and short is that the Soviet space program used actual test dummies as test dummies, and the Judica-Cordiglia recordings are, if we are to be generous, a hoax (if less generous, fraudlent).

Or were they using minorities as test dummies and getting them killed until they got it right?

The Soviets didn't single out any one group as "test dummies." Early cosmonauts were universally exposed to some horrific risks.

In fact, the Soviet space program nearly killed four cosmonauts in April 1967 on a reckless mission to test out the new Soyuz spacecraft. Despite the hundreds of known flaws with the design, the Soviet space program went ahead with the mission.

The inevitable mechanical failures inadvertently saved the lives of three men, but those same failures killed another man.

On April 24, 1967, the Soyuz 1 spacecraft crashed, killing cosmonaut Vladimir Komarov. His remains weren't even recognizable as a body (NSFW).

To add some more detail to a story that is often mis-remembered.

In early 1967, the Soviet space program was trying, and mostly failing, to get the Soyuz spacecraft to work. Sergei Korolev, the mastermind of the Soviet space program, had died in early 1966. His successors were trying to develop the most complex spacecraft they'd ever developed. And they had massive problems. Soviet engineers had to grapple with over 200 design flaws and problems with the spacecraft. They solved some of the issues, but elusive old problems were joined by plenty of new ones.

In 1966, the Soviets tested several unmanned versions of the Soyuz. The first one couldn't be launched due to several faults found during ground testing. The other vehicle, Kosmos 133, was finally launched in November 1966. Its attitude control system promptly failed, leaving it helplessly spinning in space. Ground controllers managed to regain enough control to start the re-entry process, but the barely-controlled re-entry burn sent it careening off towards China. Range control had to blow it up.

The fault-ridden first vehicle was finally fixed and readied for launch. But it blew up on the launch pad after its rocket failed in December 1966, killing a ground crewman and wrecking the pad.

Kosmos 140, launched in February 1967, did a little better. It didn't blow up on the pad. It didn't blow up on it's way to space. Its attitude control system acted up, it didn't become uncontrollable.

Well, at not totally uncontrollable. The control system failed prior to re-entry, sending the spacecraft off-course. The excessively steep re-entry burned a hole a foot wide in the heat shield and deposited the spacecraft in the ice-choked Aral Sea, hundred of miles away from its target. The scarred craft promptly sunk in 300 feet of water and had to be fished out by a team of divers.

By early 1967, the Soyuz vehicle had never been successfully tested. Every test flight would have killed anyone aboard. The Soviet space agency decided to make a manned launch anyways.

Why?

The Soyuz spacecraft was supposed to be able to carry three cosmonauts into space and support them for weeks at a time. It was a lynchpin of the Soviet's plans for a manned mission to the Moon. In early 1967, Soviet planners hoped they'd be able to use Soyuz for a manned flyby as early as July 1967 (this was progressively pushed back into 1968, 1969, and 1970 until the Soviet's manned lunar program was cancelled in the mid 1970s). They likewise hoped they could make a manned lunar landing as soon a September 1968. It was a totally unrealistic goal, given the Soviets' budgetary woes and the problems with their N1 rocket. But if they'd pulled it off, they'd have beaten or narrowly-followed the Americans to the Moon.

The Americans were putting enormous pressure on the Soviets. The Soviets had only managed two flights with their two-man Voskhod capsule between 1964 and 1965. In the same time frame, American astronauts had flown ten Gemini missions in their two-man spacecraft. Americans had gone on more spacewalks and rendezvoused with other manned spacecraft and unmanned spacecraft. The Apollo program, also making rapid progress. Apollo 1 was due to launch in March 1967 (and would have, had it not been for the fatal February 1967 fire). The Saturn rockets were working well and several unmanned tests would go ahead as planned in late 1967.

Soviet leadership didn't want to get beaten in the Space Race. May Day 1967 was coming up, one of the most important holidays in the Soviet Union. A triumphant cosmonaut sitting next to Brezhnev watching the massive parade in Red Square would be a satisfying propaganda coup. Perfect for celebrating the 50th Anniversary of the Bolshevik Revolution coming later that year.

Vasilii Pavlovich Mishin, director of the TsKBEM bureau that ran the Soyuz program, later complained:

Truly, there never was a time when we worked in peace, without being hurried or pressured from above. The unskilled, totally bewildered, high-ranking bureaucrats believe that they are fulfilling their duties if they are shouting “Let’s go, let’s go!” at people who don't even have time to wipe the sweat off their brows.

So someone was going to go up in Soyuz 1. That person would be Vladimir Komarov.

To up the ante, Soyuz 2 would also be launched at the same time, with cosmonauts Valeri Bykovsky, Alexei Yeliseyev, and Yevgeni Khrunov aboard. Soyuz 1 and 2 were supposed to rendezvous in space. Then, Yeliseyev and Khrunov would spacewalk over the Soyuz 1 and return to Earth with Komarov. Bykovsky would return home alone in Soyuz 2.

In and of itself, this was a bad idea. Not only was it highly ambitious to launch two unproven, fault-ridden spacecraft at the same time, the mission called for two highly challenging tasks: orbital rendezvous and a spacewalk. Soyuz's history of control problems made the rendezvous highly risky. Another design flaw made the spacewalk even riskier.

Ground tests had shown it was hard for a cosmonaut to get out of Soyuz's tiny hatch. Getting back in might be impossible. During his spacewalk on the Voskhod 2 mission in 1965, Alexei Leonov had nearly been trapped in space. His spacesuit had ballooned in the vacuum of space. He was only able to get back in by venting much of the air from his suit. If something similar happened on the first Soyuz mission, there was a very real chance Yeliseyev and Khrunov would be trapped in space on their spacewalk, unable to get back into the spacecraft.

Vladimir Mikhaylovich Komarov was one of the most impressive of the already-impressive early pilot-cosmonauts. He had the most rigorous academic background. He was a graduate of the prestigious Soviet Air Force Academy, an accomplishment shared by only one of his peers. Uniquely, he was a test pilot and an engineer.* He'd helped design the Vostok and Voskhod spacecraft, and he'd taken the Voskhod 1 spacecraft into orbit on its maiden flight in 1964. Yuri Gagarin had even jokingly nicknamed the academically-gifted Komarov "The Professor."

Even among these high achievers, Komarov was already a standout. By all accounts he was conscientious, highly intelligent, modest and reserved, and one of the most erudite of the cosmonauts.

*Most American astronauts at this point were test pilots and engineers, with a handful of exceptions, like John Glenn --who was "just" a record-breaking test pilot.

The point being, Komarov almost certainly knew Soyuz 1 wasn't safe. As an engineer, he was familiar with its design flaws. As a pilot, he knew its control issues were serious.