Added // TODO and updated READMEs

javafx-template/src/test/java/app/README.md

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+# Tests for the RPN calculator
+
+This folder/package contains tests based on TestFX for the RPN Calculator (currently only one test class).
+
+As can be seen when launching, the app contains a list (top) showing the operands
+(topmost operand at the bottom), a text field (below list, initially empty) for a new operand and
+the buttons for digits, enter, decimal point, operations etc.
+
+## What is tested
+
+The tests simulate clicks on the buttons and checks that the underlying Calc object,
+the list (a view of the Calc object's operand stack) and the text field are updated as expected.
+E.g. if you click buttons `2 3 . 5` the string `23.5` should be shown,
+while the list is not affected. If you then click `enter`, the text field should be emptied, the operand stack should have `23.5` at the top and the list should have `23.5` at the bottom 
+(logically the top of the operand stack).
+
+Below are the specific cases that are tested.
+
+buttons to click `=>` text field content:
+
+- `2 7` => `27`
+- `2 7 .` => `27.`
+- `2 7 . 5` => `27.5`
+- `2 7 . 5 .` => `27.` (cut at decimal point)
+
+buttons to click `=>` operand stack/list content (from the bottom):
+
+- `2 7 . 5 enter"` => `27.5`
+- `2 7 enter` => `27.0"`
+- `2 enter 7 enter 5 enter` => `5.0 7.0 2.0` 
+- `2 7 . enter` => `27.0` 
+- `2 7 . 5 enter` => `27.5` 
+- `2 enter 7 +` => `9.0` 
+- `2 enter 7 -` => `-5.0` 
+- `2 enter 7 *` => `14.0` 
+- `6 enter 3 /` => `2.0` 
+- `2 5 enter √` => `5.0` 
+- `π` => `3.1415...` (the value of the `Math.PI` constant)