atlas tool: testing via mocking (#18588)

* atlas: refactoring
* Atlas: do some basic testing via mocking

tools/atlas/tests/balls.nimble

@@ -0,0 +1,32 @@
+version = "3.4.1"
+author = "disruptek"
+description = "a unittest framework with balls 🔴🟡🟢"
+license = "MIT"
+
+# requires newTreeFrom
+requires "https://github.com/disruptek/grok >= 0.5.0 & < 1.0.0"
+requires "https://github.com/disruptek/ups < 1.0.0"
+requires "https://github.com/planetis-m/sync >= 1.0.0 & < 2.0.0"
+#requires "https://github.com/c-blake/cligen < 2.0.0"
+
+bin = @["balls"]            # build the binary for basic test running
+installExt = @["nim"]       # we need to install balls.nim also
+skipDirs = @["tests"]       # so stupid...  who doesn't want tests?
+#installFiles = @["balls.nim"] # https://github.com/nim-lang/Nim/issues/16661
+
+task test, "run tests for ci":
+  when defined(windows):
+    exec "balls.cmd"
+  else:
+    exec "balls"
+
+task demo, "produce a demo":
+  exec "nim c --define:release balls.nim"
+  when (NimMajor, NimMinor) != (1, 0):
+    echo "due to nim bug #16307, use nim-1.0"
+    quit 1
+  exec """demo docs/demo.svg "nim c --out=\$1 examples/fails.nim""""
+  exec """demo docs/clean.svg "nim c --define:danger -f --out=\$1 tests/test.nim""""
+  exec "nim c --define:release --define:ballsDry balls.nim"
+  exec """demo docs/runner.svg "balls""""
+