tests/motion:: ensure stepTimerQuantum is always respected

This catches motion stutters as fixed in
502f42b7be

tests/unit/modules/motion/rampgen.cpp

@@ -34,7 +34,8 @@ int main(int argc, const char *argv[]) {
     const int maxJerk = 1;
 
     // write common parameters
-    fprintf(fd, "{\"timebase\": %lu}\n", F_CPU / config::stepTimerFrequencyDivider);
+    fprintf(fd, "{\"timebase\": %lu, \"quantum\": %u}\n",
+        F_CPU / config::stepTimerFrequencyDivider, config::stepTimerQuantum);
 
     for (int ax_cnt = 0; ax_cnt != 2; ++ax_cnt) {
         for (int accel = 2000; accel <= 50000; accel *= 2) {

tests/unit/modules/motion/test_motion_ramp.py

@@ -156,6 +156,15 @@ def check_run(info, run):
     ax_info, data = run
     ax_count = len(ax_info)
 
+    # first and last interval should always be zero
+    assert (data[0][1] == 0)
+    assert (data[-1][1] == 0)
+
+    # ensure no interval is shorter than the specified quantum
+    for i in range(1, len(data) - 2):
+        interval = data[i][1]
+        assert (interval >= info['quantum'])
+
     # split axis information
     ax_data = []
     for ax in range(ax_count):