v4, 7 partsImprovements for t/README

diff --git a/t/README b/t/README
index aa4ed28..cad6fde 100644
--- a/t/README
+++ b/t/README
@@ -221,9 +221,10 @@ This test harness library does the following things:
  - If the script is invoked with command line argument --help
    (or -h), it shows the test_description and exits.
 
- - Creates an empty test directory with an empty .git/objects
-   database and chdir(2) into it.  This directory is 't/trash directory'
-   if you must know, but I do not think you care.
+ - Creates an empty test directory with an empty .git/objects database
+   and chdir(2) into it.  This directory is 't/trash
+   directory.$test_name_without_dotsh', with t/ subject to change by
+   the --root option documented above.
 
  - Defines standard test helper functions for your scripts to
    use.  These functions are designed to make all scripts behave

diff --git a/t/README b/t/README
index cad6fde..a7312fa 100644
--- a/t/README
+++ b/t/README
@@ -33,7 +33,7 @@ the tests.
     ok 3 - plain bare
 
 Since the tests all output TAP (see http://testanything.org) they can
-be run with any TAP harness. Here's an example of paralell testing
+be run with any TAP harness. Here's an example of parallel testing
 powered by a recent version of prove(1):
 
     $ prove --timer --jobs 15 ./t[0-9]*.sh

diff --git a/t/README b/t/README
index a7312fa..c1fd092 100644
--- a/t/README
+++ b/t/README
@@ -246,9 +246,9 @@ Test harness library
 There are a handful helper functions defined in the test harness
 library for your script to use.
 
- - test_expect_success <message> <script>
+ - test_expect_success [<prereq>] <message> <script>
 
-   This takes two strings as parameter, and evaluates the
+   Usually takes two strings as parameter, and evaluates the
    <script>.  If it yields success, test is considered
    successful.  <message> should state what it is testing.
 
@@ -258,7 +258,14 @@ library for your script to use.
 	    'git-write-tree should be able to write an empty tree.' \
 	    'tree=$(git-write-tree)'
 
- - test_expect_failure <message> <script>
+   If you supply three parameters the first will be taken to be a
+   prerequisite, see the test_set_prereq and test_have_prereq
+   documentation below:
+
+	test_expect_success TTY 'git --paginate rev-list uses a pager' \
+	    ' ... '
+
+ - test_expect_failure [<prereq>] <message> <script>
 
    This is NOT the opposite of test_expect_success, but is used
    to mark a test that demonstrates a known breakage.  Unlike
@@ -267,6 +274,9 @@ library for your script to use.
    success and "still broken" on failure.  Failures from these
    tests won't cause -i (immediate) to stop.
 
+   Like test_expect_success this function can optionally use a three
+   argument invocation with a prerequisite as the first argument.
+
  - test_debug <script>
 
    This takes a single argument, <script>, and evaluates it only
@@ -299,6 +309,27 @@ library for your script to use.
    Merges the given rev using the given message.  Like test_commit,
    creates a tag and calls test_tick before committing.
 
+ - test_set_prereq SOME_PREREQ
+
+   Set a test prerequisite to be used later with test_have_prereq. The
+   test-lib will set some prerequisites for you, e.g. PERL and PYTHON
+   which are derived from ./GIT-BUILD-OPTIONS (grep test_set_prereq
+   test-lib.sh for more). Others you can set yourself and use later
+   with either test_have_prereq directly, or the three argument
+   invocation of test_expect_success and test_expect_failure.
+
+ - test_have_prereq SOME PREREQ
+
+   Check if we have a prerequisite previously set with
+   test_set_prereq. The most common use of this directly is to skip
+   all the tests if we don't have some essential prerequisite:
+
+	if ! test_have_prereq PERL
+	then
+	    skip_all='skipping perl interface tests, perl not available'
+	    test_done
+	fi
+
 Tips for Writing Tests
 ----------------------
 

diff --git a/t/README b/t/README
index c1fd092..b40403d 100644
--- a/t/README
+++ b/t/README
@@ -330,6 +330,33 @@ library for your script to use.
 	    test_done
 	fi
 
+ - test_external [<prereq>] <message> <external> <script>
+
+   Execute a <script> with an <external> interpreter (like perl). This
+   was added for tests like t9700-perl-git.sh which do most of their
+   work in an external test script.
+
+	test_external \
+	    'GitwebCache::*FileCache*' \
+	    "$PERL_PATH" "$TEST_DIRECTORY"/t9503/test_cache_interface.pl
+
+   If the test is outputting its own TAP you should set the
+   test_external_has_tap variable somewhere before calling the first
+   test_external* function. See t9700-perl-git.sh for an example.
+
+	# The external test will outputs its own plan
+	test_external_has_tap=1
+
+ - test_external_without_stderr [<prereq>] <message> <external> <script>
+
+   Like test_external but fail if there's any output on stderr,
+   instead of checking the exit code.
+
+	test_external_without_stderr \
+	    'Perl API' \
+	    "$PERL_PATH" "$TEST_DIRECTORY"/t9700/test.pl
+
+
 Tips for Writing Tests
 ----------------------
 

diff --git a/t/README b/t/README
index b40403d..04ad927 100644
--- a/t/README
+++ b/t/README
@@ -277,6 +277,13 @@ library for your script to use.
    Like test_expect_success this function can optionally use a three
    argument invocation with a prerequisite as the first argument.
 
+ - test_expect_code [<prereq>] <code> <message> <script>
+
+   Analogous to test_expect_success, but pass the test if it exits
+   with a given exit <code>
+
+ test_expect_code 1 'Merge with d/f conflicts' 'git merge "merge msg" B master'
+
  - test_debug <script>
 
    This takes a single argument, <script>, and evaluates it only

diff --git a/t/README b/t/README
index 04ad927..4079635 100644
--- a/t/README
+++ b/t/README
@@ -231,6 +231,18 @@ This test harness library does the following things:
    consistently when command line arguments --verbose (or -v),
    --debug (or -d), and --immediate (or -i) is given.
 
+Skipping tests
+--------------
+
+If you need to skip all the remaining tests you should set skip_all
+and immediately call test_done. The string you give to skip_all will
+be used as an explanation for why the test was skipped. for instance:
+
+	if ! test_have_prereq PERL
+	then
+	    skip_all='skipping perl interface tests, perl not available'
+	    test_done
+	fi
 
 End with test_done
 ------------------

diff --git a/t/README b/t/README
index 4079635..e481657 100644
--- a/t/README
+++ b/t/README
@@ -231,6 +231,84 @@ This test harness library does the following things:
    consistently when command line arguments --verbose (or -v),
    --debug (or -d), and --immediate (or -i) is given.
 
+Do's, don'ts & things to keep in mind
+-------------------------------------
+
+Here's a few examples of things you probably should and shouldn't do
+when writing tests.
+
+Do:
+
+ - Put as much code as possible inside test_expect_success and other
+   assertions.
+
+   Even code that isn't a test per se, but merely some setup code
+   should be inside a test assertion if at all possible. Test scripts
+   should only have trivial code outside of their assertions.
+
+ - Chain your test assertions
+
+   Write test code like this:
+
+	git merge foo &&
+	git push bar &&
+	test ...
+
+   Instead of:
+
+	git merge hla
+	git push gh
+	test ...
+
+   That way all of the commands in your tests will succeed or fail. If
+   you must ignore the return value of something (e.g. the return
+   value of export is unportable) it's best to indicate so explicitly
+   with a semicolon:
+
+	export HLAGH;
+	git merge hla &&
+	git push gh &&
+	test ...
+
+Don't:
+
+ - exit() within a <script> part.
+
+   The harness will catch this as a programming error of the test.
+   Use test_done instead if you need to stop the tests early (see
+   "Skipping tests" below).
+
+ - Break the TAP output
+
+   The raw output from your test might be interpreted by a TAP
+   harness. You usually don't have to worry about that. TAP harnesses
+   will ignore everything they don't know about, but don't step on
+   their toes in these areas:
+
+   - Don't print lines like "$x..$y" where $x and $y are integers.
+
+   - Don't print lines that begin with "ok" or "not ok".
+
+   A TAP harness expect a line that begins with either "ok" and "not
+   ok" to signal a test passed or failed (and our harness already
+   produces such lines), so your script shouldn't emit such lines to
+   their output.
+
+   You can glean some further possible issues from the TAP grammar
+   (see http://search.cpan.org/perldoc?TAP::Parser::Grammar#TAP_Grammar)
+   but the best indication is to just run the tests with prove(1),
+   it'll complain if anything is amiss.
+
+Keep in mind:
+
+ - That what you print to stderr and stdout is usually ignored
+
+   Inside <script> part, the standard output and standard error
+   streams are discarded, and the test harness only reports "ok" or
+   "not ok" to the end user running the tests. Under --verbose, they
+   are shown to help debugging the tests.
+
+
 Skipping tests
 --------------