fixes #2974

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+Writing tests
+=============
+
+Not all the tests follow this scheme, feel free to change the ones
+that don't. Always leave the code cleaner than you found it.
+
+Stdlib
+------
+
+If you change the stdlib (anything under ``lib/``), put a test in the
+file you changed. Add the tests under an ``when isMainModule:``
+condition so they only get executed when the tester is building the
+file. Each test should be in a separate ``block:`` statement, such that
+each has its own scope. Use boolean conditions and ``doAssert`` for the
+testing by itself, don't rely on echo statements or similar.
+
+Sample test:
+
+.. code-block:: nim
+
+  when isMainModule:
+    block: # newSeqWith tests
+      var seq2D = newSeqWith(4, newSeq[bool](2))
+      seq2D[0][0] = true
+      seq2D[1][0] = true
+      seq2D[0][1] = true
+      doAssert seq2D == @[@[true, true], @[true, false],
+                          @[false, false], @[false, false]]
+
+Compiler
+--------
+
+The tests for the compiler work differently, they are all located in
+``tests/``. Each test has its own file, which is different from the
+stdlib tests. At the beginning of every test is the expected side of
+the test. Possible keys are:
+
+- output: The expected output, most likely via ``echo``
+- exitcode: Exit code of the test (via ``exit(number)``)
+- errormsg: The expected error message
+- file: The file the errormsg
+- line: The line the errormsg was produced at
+
+An example for a test:
+
+.. code-block:: nim
+
+  discard """
+    errormsg: "type mismatch: got (PTest)"
+  """
+
+  type
+    PTest = ref object
+
+  proc test(x: PTest, y: int) = nil
+
+  var buf: PTest
+  buf.test()
+
+Running tests
+=============
+
+You can run the tests with
+
+::
+  ./koch tests
+
+which will run a good subset of tests. Some tests may fail. If you
+only want to see the output of failing tests, go for
+
+::
+  ./koch tests --failing all
+
+You can also run only a single category of tests. A category is a subdirectory
+in the ``tests`` directory. There are a couple of special categories; for a
+list of these, see ``tests/testament/categories.nim``, at the bottom.
+
+::
+  ./koch tests c lib
+
+Comparing tests
+===============
+
+Because some tests fail in the current ``devel`` branch, not every fail
+after your change is necessarily caused by your changes.
+
+The tester can compare two test runs. First, you need to create the
+reference test. You'll also need to the commit id, because that's what
+the tester needs to know in order to compare the two.
+
+::
+  git checkout devel
+  DEVEL_COMMIT=$(git rev-parse HEAD)
+  ./koch tests
+
+Then switch over to your changes and run the tester again.
+
+::
+  git checkout your-changes
+  ./koch tests
+
+Then you can ask the tester to create a ``testresults.html`` which will
+tell you if any new tests passed/failed.
+
+::
+  ./koch --print html $DEVEL_COMMIT
+
+
+Deprecation
+===========
+
+Backward compatibility is important, so if you are renaming a proc or
+a type, you can use
+
+
+.. code-block:: nim
+
+  {.deprecated: [oldName: new_name].}
+
+Or you can simply use
+
+.. code-block:: nim
+
+  proc oldProc() {.deprecated.}
+
+to mark a symbol as deprecated. Works for procs/types/vars/consts,
+etc. Note that currently the ``deprecated`` statement does not work well with
+overloading so for routines the latter variant is better.
+
+
+`Deprecated <http://nim-lang.org/docs/manual.html#pragmas-deprecated-pragma>`_
+pragma in the manual.
+
+
+
+The Git stuff
+=============
+
+General commit rules
+--------------------
+
+1. All changes introduced by the commit (diff lines) must be related to the
+   subject of the commit.
+
+   If you change some other unrelated to the subject parts of the file, because
+   your editor reformatted automatically the code or whatever different reason,
+   this should be excluded from the commit.
+
+   *Tip:* Never commit everything as is using ``git commit -a``, but review
+   carefully your changes with ``git add -p``.
+
+2. Changes should not introduce any trailing whitespace.
+
+   Always check your changes for whitespace errors using ``git diff --check``
+   or add following ``pre-commit`` hook:
+
+   .. code-block:: sh
+
+      #!/bin/sh
+      git diff --check --cached || exit $?
+
+   No sane programming or markup language cares about trailing whitespace, so
+   tailing whitespace is just a noise you should not introduce to the
+   repository.
+
+3. Describe your commit and use your common sense.