Adds smaller code samples from Chapters 1-3 to the tester.

tests/niminaction/Chapter3/various3.nim

@@ -0,0 +1,93 @@
+import threadpool
+proc foo: string = "Dog"
+var x: FlowVar[string] = spawn foo()
+assert(^x == "Dog")
+
+block:
+  type
+    Box = object
+      case empty: bool
+      of false:
+        contents: string
+      else:
+        discard
+
+  var obj = Box(empty: false, contents: "Hello")
+  assert obj.contents == "Hello"
+
+  var obj2 = Box(empty: true)
+  doAssertRaises(FieldError):
+    echo(obj2.contents)
+
+import json
+assert parseJson("null").kind == JNull
+assert parseJson("true").kind == JBool
+assert parseJson("42").kind == JInt
+assert parseJson("3.14").kind == JFloat
+assert parseJson("\"Hi\"").kind == JString
+assert parseJson("""{ "key": "value" }""").kind == JObject
+assert parseJson("[1, 2, 3, 4]").kind == JArray
+
+import json
+let data = """
+  {"username": "Dominik"}
+"""
+
+let obj = parseJson(data) 
+assert obj.kind == JObject 
+assert obj["username"].kind == JString 
+assert obj["username"].str == "Dominik"
+
+block:
+  proc count10(): int =
+    for i in 0 .. <10:
+      result.inc
+  assert count10() == 10
+
+type
+  Point = tuple[x, y: int]
+
+var point = (5, 10)
+var point2 = (x: 5, y: 10)
+
+type
+  Human = object
+    name: string
+    age: int
+
+var jeff = Human(name: "Jeff", age: 23)
+var amy = Human(name: "Amy", age: 20)
+
+import asyncdispatch
+
+var future = newFuture[int]() 
+doAssert(not future.finished) 
+
+future.callback = 
+  proc (future: Future[int]) = 
+    echo("Future is no longer empty, ", future.read) 
+
+future.complete(42)
+
+import asyncdispatch, asyncfile
+
+when false:
+  var file = openAsync("")
+  let dataFut = file.readAll()
+  dataFut.callback =
+    proc (future: Future[string]) =
+      echo(future.read())
+
+  asyncdispatch.runForever()
+
+import asyncdispatch, asyncfile, os
+
+proc readFiles() {.async.} =
+  # --- Changed to getTempDir here.
+  var file = openAsync(getTempDir() / "test.txt", fmReadWrite)
+  let data = await file.readAll() 
+  echo(data) 
+  await file.write("Hello!\n") 
+
+waitFor readFiles()
+