Back in the earliest days (probably before most of the readers here were born, around 1958., there was no distinction between testers and developers. They were all called programmers, and the best of them were chosen for our test group (ours, on Project Mercury, was the first test group that I know of).
Our test group was copied for a number of IBM Federal Systems projects, but over the years, people started having a different sort of test group. These groups were not made up of programmers, but were largely chosen because they would be cheaper than programmers. It was widely believed that any idiot could do testing. Many times I heard managers say they could train monkeys to sit around banging on keys.
Since that time, gradually over the years, more managers have come (ever so slowly) to realize that testing is a specialty that requires special people with special training and talent. We still have many “monkey-managers,” and for those managers, the role of testers has not changed much. But where professional testing is valued for itself, yes, the roles of tester and developer have become more similar (though not identical).
BTW, the role of monkeys hasn’t changed much, but, then, some developers play that role very well.
My father gave me a slide rule when I was about 7 years old. I used it to compute baseball batting averages, which was what motivated me at that time in my life. I still have that slide rule. It's a small, cheap slide rule, made from bamboo with plastic (or maybe ivory) faces. He bought them in quantity to give to the young ladies who computed customer bills for Sears, when my father worked for 20+ years, improving processes. The slide rules were used to check their multiplications, preventing enormous numbers of errors that had previously been sent to customers.
The next interactions were with tables of sines, cosines, and logarithms, used for more precise calculations, mostly in math classes and personal experimenting with numbers for fun.
At age 11, still in Chicago, I read a magazine article about computers, then familiarly known as "giant brains." By this time, I had been label as s "brainy" kid, and I longed to learn more about brains. I determined that computers were what I wanted to do with my life—and they turned out to be. I didn't know anyone who had ever seen a computer, let alone used one.
I watched and waited for signs of a computer, but went all through high school without seeing one. Well, not exactly. I had a summer night job in a large bakery computing recipe requirements for the following day's orders. I used a Monroe adding machine.
When I entered college at 16, I told the counselors I wanted to work with computers, but none of them knew anything about computers other than they had something to do with electrical engineering and physics. They decided I should major in Physics, because I was good in math, which would be "wasted in EE." One day, I saw a notice for a "computing course" using Monroe adding machines, given by the Monroe company. I was a short course, and I already knew most the material better than the instructor. But I passed, earning a certificate that I've lost somewhere along the way. It's the only computing course I ever took, and the only "degree" in computing that I ever earned.
My next encounter with a computer was when I looked in the mirror. I got a job in the Physics department as a "computer"—that was my job title. I was shown a Friden electromechanical calculator, which I used along with pencil and paper (and eraser) to invert 10 by 10 matrices for faculty members.
I graduated with honors in Physics, Math, Philosophy, and English, then went to Berkeley to study graduate Physics. I was perhaps two months from a doctorate in Physics (exams passed, thesis experiments finished and waiting to be written up), but I read an IBM ad in Physics Today looking for problem solvers. The ad described the work I had dreamed of since age 11, so I wrote to IBM and was hired as an Applied Science Representative—on June 1, 1956.
I was given no training, but my first assignment was to teach a programming course to three other new Applied Science Representatives who were to join IBM in San Francisco two weeks later. (I had a wife and 1.66 kids by then, so I needed the two-weeks pay, so I started early.) The first machine I encountered was an IBM 607, which was a wired program machine with 20 wired program steps (this was the expanded version) and one signed ten-digit number of data storage. In my first week, using the library of manuals, I mastered that machine plus a bunch of older punched-card machines.
I spent the next week learning to program the IBM 650, a stored program machine that kept programs and data on a magnetic drum, but had wired control panels for input and output formatting. This was all theoretical, as there was no IBM 650 anywhere in San Francisco yet. When one finally arrived shortly thereafter, it was the first stored program machine I had ever seen.
While waiting for the 650's arrival, I earned a reputation as a "whiz kid" (the term "programmer" wasn't yet in use) by making the 607 do tricks. My most impressive trick was turning on all the lights on the 607 control panel, which won me a dollar bet.
When the 650 arrived, I immediately tried out a program I had written to compute tables of sines, cosines, and logarithms. With the arrival of computers, such tables were now totally useless, but I was in nerd-heaven. I was being paid $450 a month for playing with the world's greatest toy, a job I would gladly have paid $450 a month to do—though I wisely didn't tell IBM that.