Test cricket has historically been the most perfect 'Test' for cricketing abilities. A team has to be superior in terms of temperament, mentality, dedication, endurance and intelligence along with technique and consistency in order to defeat the opposition in Test cricket. In other words, there is no 'fluke' in this format of the game.
However, with the changes in cricket like introduction of newer formats, change in bat sizes, new rules brought, etc, Test cricket has evolved like every other thing in the world.
To analyze the evolution of the challenges in Test cricket, we can divide it into eras like pre-1990s, 1990-2000, 2000-2019, 2019 (since the advent of ICC World Test Championship) and onwards etc. by taking the following factors into consideration -
Pitch and weather conditions, Batting, Fast-bowling, Spin-bowling and the Number of teams competing at a higher level.
Pitch and weather conditions
Pre-2000: The pitches and conditions were more predictable then. The Indian tracks were typically flat with some cracks, grounds like the Lord's offered swinging conditions and those in Australia offered bounce. The batters had to master their shot selections accordingly.
2000 and onwards: The unpredictability of the pitch conditions have increased. The teams are generally more into enjoying the home advantage, though there is uncertainty. The captains are often in a dilemma whether to bat or bowl first.
The sub-continental Tests are often played on rank turners which typically help the spinners, who have been one of the main strengths of teams like Bangladesh for more than decades.
From Day-1 to Day-5, it gradually converts into a minefield making life difficult for the batters.
The same happens with the sub-continental batters travelling to SENA, as the teams with plenty of quality seamers take the advantage of extremely swinging-conditions, even if the ground has a reputation of producing batting-friendly pitches.
In the ‘70s and ‘80s, the batters did not enjoy the privilege of the protections that the modern batters do. Legends like Sir Viv Richards played without helmets. Batting used to be more defensive, the batters had a habit of playing late against the fast bowlers of that era, the innings were long and most of the competitive matches ended in a draw.
In the post 2000 era, the batting standards took a turn towards a bit more aggression in order to produce the results in favour of the team.
The batters adapting to the shortest format of the game since the late 2000s plays a huge part behind it. Though the early 2000s were not that different from the 1990s in terms of batting, the 2010s showed the evolution clearly.
It is said that the knocks like Brian Lara's 400 will never be repeated because of these changes, as the captains are more focused on producing the results.
Since the advent of the ICC World Test Championship in 2019, winning the Tests has become a necessity to finish higher in the WTC standings. We see a lot of knocks with a strike rate of about 80-100, adding a significant amount of runs in a short time; Rishabh Pant's quick innings would be a perfect example.
Apart from these changes, the bat quality and size have increased over the years, with rules like a maximum of 2 bouncers being allowed in modern cricket.
But there are new challenges for the batters too, like surviving the 5th day rank turners, responding to the new tricks of the seamers, which takes us to the next topic of the analysis,
Before 2000, especially in the ‘70s and ‘80s, there was a mentionable availability of bowlers with express pace.
There were the likes of Jeff Thomson, Michael Holding, Dennis Lillee, Malcolm Marshall and many more. Bowlers like them meant absolute terror for the batters, as they swung it with express pace, often opting for a deadly bouncer. The batting used to be more defensive because of them.
In the 2000s, there were seamers like Glenn McGrath, Brett Lee, Shoaib Akhtar and James Anderson. The Shoaibs and Bretts can be categorised into the express-pace group because of their pace, but even they were more 'crafty' than the fast bowlers from the previous era.
Andreson, McGrath and from the mid-2000s, Dale Steyn were more 'smart' than deadly, tending to set a batter up by swinging it in both directions and using the reverse-swing with the old ball.
The modern seamers having hectic schedules conserve themselves for a longer career. The likes of Jofra Archer have been seen bowling with a lower pace compared to the full capacity in Test cricket.
Seamers like James Anderson can maintain their fitness and build a long career, for decades, which was not the regular case before 2000.
Spin-bowling took a turn into a whole new level with the advent of Shane Warne and Muttiah Muralitharan in the 1990s. Before them, most of the specialist spinners relied on the accuracy, flight and turn. But Warne took his variations with the flipper and wrong-uns to the next level in the late 1990s.
Muthiah Muralitharan's variations like the Doosra did not only help him dominate and become one of the greatest, it was followed by the spinners of the next generation as well.
In the 2010s, Graeme Swann, Nathan Lyon, Ravichandran Ashwin continued the trend of bowling with variations. They would constantly flight it on the off-stump, taking it away from the left hander, and suddenly come up with the arm-ball.
In other words, Warne and Muralitharan, two greatest spinners of all time paved the way for the next generation spinners and made the game more challenging for the batters.
Increase of teams competing at a higher level
With the globalisation of cricket, more teams have gained Test Statuses after the 2000s. Let's take Bangladesh for an example.
Teams like Bangladesh that never played Tests before 2000 were being invited to tour countries like Pakistan in the early 2000s.
Fast forward to 2016, The country eventually won a match against England at home before defeating their rivals, Australia in 2017, in their own way, creating rank-turners. So, it's not always easy for the higher-ranked teams to stay afloat in such tours.
The ICC World Test Championship was introduced in 2019, and it makes sure that the participating teams play the teams of every level, at home and away from home, in every edition. Bangladesh's win against the inaugural WTC champions, New Zealand at their own backyard explains the necessity of this change.
To conclude, the pitches have become more unpredictable, the batting has new privileges as well as challenges, fast bowling is more conserved as well as more skillful, the spin bowling has modern variations and there are new teams competing at a higher level than before and often winning in the modern days of Test cricket.
So whether Test cricket has become more challenging over the decades or not is a topic of everlasting debate.