Update and refine the readme

Author: NickVolynkin

README.md

@@ -2,51 +2,117 @@
 
 [![Coverage Status](https://coveralls.io/repos/github/tarantool/test-run/badge.svg)](https://coveralls.io/github/tarantool/test-run)
 
-### Test Suite
-
-Bunch of tests, that lay down in the subfolder (recursively) with `suite.ini`
-file. `suite.ini` is basic ini-file, that consists of one section `default`,
-and a number of fields:
-
-* `core`
-* `description` - Test Suite description
-* `script` - shebang file to start tarantool with
-* disables:
-    * `disabled` - tests that must be skipped
-    * `release_disabled` - tests that must be skipped when Tarantool has been
-      builded with `Release`
-    * `valgrind_disabled` - tests that must be skipped when Valgrind is enabled
-* `lua_libs` - paths for lua files, that should be copied into the folder,
-  where server is started (delimited with the space, e.g. `lua_libs=lua/1.lua
-  lua/2.lua`)
-* `long_run` - mark tests as long, enabled only with `--long` option (delimited
-  with the space, e.g. `long_run=t1.test.lua t2.test.lua`)
-* `config` - test configuration file name
-
-Field `core` must be one of:
-
-* `tarantool` - Test-Suite for Functional Testing
-* `app` - Another functional Test-Suite
-* `unittest` - Unit-Testing Test Suite
-
-### Test
-
-Each test consists of files `*.test(.lua|.sql|.py)?`, `*.result`, and may have
-skip condition file `*.skipcond`.  On first run (without `.result`) `.result`
-is generated from output.  Each run, in the beggining, `.skipcond` file is
-executed. In the local env there's object `self`, that's `Test` object. If test
-must be skipped - you must put `self.skip = 1` in this file. Next,
-`.test(.lua|.py)?` is executed and file `.reject` is created, then `.reject` is
-compared with `.result`. If something differs, then 15 last string of this diff
-file are printed and `.reject` file is saving in the `<vardir>/rejects/<suite>`
-subfolder given in options or set localy as `var/rejects/<suite>` by default.
-If not, then `.reject` file is deleted.
+## Test suite configuration
+
+Test suite is a bunch of tests located in a subdirectory (recursively) with a `suite.ini`
+file. The `suite.ini` is a basic ini-file with one section `[default]`.
+
+```ini
+[default]
+core = luatest
+description = Example test suite using luatest
+; comment line
+...
+```
+
+All list values in `suite.ini` are delimited by spaces.
+Lines starting with `;` are comment lines.
+
+Below is a list of configuration values (fields) in the `suite.ini` file.
+
+### General configuration
+
+* `core` — major testing dependency or method
+  Should have one of the following values:
+
+  * `tarantool` — test suite used for functional testing
+  * `app` — TAP-tests, another functional test suite
+  * `unittest` — unit testing test suite
+  * `luatest` — test suite using luatest library
+
+* `description` — test suite description
+* `script` (optional) — shebang file to start tarantool with
+* `config` — name of a test configuration file
+  TODO: what's a test configuration file?
+
+### Skipping tests
+
+A number of fields are used to disable (skip) certain tests:
+
+* `disabled` — list of tests that should be skipped
+* `release_disabled` — list of tests that should be skipped when Tarantool is
+    built with `Release`
+* `valgrind_disabled` — list of tests that should be skipped when Valgrind is enabled
+* `long_run` — mark tests as long, such tests will run only with `--long` option.
+
+  ```ini
+  long_run = t1.test.lua t2.test.lua
+  ```
+
+### Other parameters
+
+* `lua_libs` — paths for lua files, that should be copied into the folder,
+  where server is started. For example:
+
+  ```ini
+  lua_libs = lua/require_mod.lua lua/serializer_test.lua lua/process_timeout.lua
+  ```
+
+* `show_reproduce_content` (optional, `True` by default) — TODO: what's this?
+* `is_parallel` (optional, `False` by default) — whether the tests in the suite can run in parallel
+
+* `use_unix_sockets_iproto` (optional, `False` by default) — use hard-coded unix sockets
+* `use_unix_sockets_iproto` (optional, `False` by default) — use hard-coded unix sockets for iproto.
+  This parameter is specific to `core = app`.
+
+### Fragile tests
+
+Tests which fail sometimes due to external reasons can be marked as fragile (flaky).
+Test-run will retry each test if it fails.
+It's recommended to provide a list of related
+[tarantool/tarantool](https://github.com/tarantool/tarantool) issues
+next to each fragile test.
+
+```ini
+fragile = {
+    "retries": 10,
+    "tests": {
+        "tarantoolctl.test.lua": {
+            "issues": [ "gh-5059", "gh-5346" ],
+        },
+        {...},
+        {...},
+    }
+}
+```
+
+## Steps of a test run
+
+Each test consists of files `*.test(.lua|.sql|.py)?`, `*.result`,
+and an optional skip condition file `*.skipcond`.
+
+In the beginning of each test run, the `.skipcond` file is executed as a Python script.
+In the local Python environment there's a `self` object, which is an instance of the [`Test` class](./lib/test.py).
+To skip the test under some condition, set `self.skip = 1`.
+
+Next, the test in `.test(.lua|.py)?` is executed. 
+If this is a first test run and there's no `.result` file yet, it is generated from the output.
+If there is a `.result` file, output is written to a `.reject` file,
+which is then compared to `.result`.
+
+If there's a difference between `.reject` and `.result`, the following happens:
+
+1. The last 15 lines of diff are printed to output.
+2. The `.reject` file is saved in the `<vardir>/rejects/<suite>`
+   subfolder given in options or set locally as `var/rejects/<suite>` by default.
+
+If there is no difference between `.reject` and `.result`, the `.reject` file is deleted.
 
 ### Test configuration
 
-Test configuration file contains config for multiple run. For each test section
-system runs separated test and compares result with common `.result` file. For
-example we need to run one test for different db engines("*" means default
+Test configuration file contains configuration for multiple runs.
+For each test section, system runs a separate test and compares the result to the common `.result` file.
+For  example, we need to run a test with different DB engines (`"*"` means the default
 configuration):
 
 ```json
@@ -62,15 +128,15 @@ configuration):
 }
 ```
 
-In test case we can get configuration from inspector:
+In the test case we can get configuration from the inspector:
 
 ```lua
 engine = test_run:get_cfg('engine')
 -- first run engine is 'memtx'
 -- second run engine is 'sophia'
 ```
 
-"engine" value has a special meaning for *.test.sql files: if it is "memtx" or
+"engine" value has a special meaning for `*.test.sql` files: if it is "memtx" or
 "vinyl", then the corresponding default engine will be set before executing
 commands from a test file. An engine is set with the following commands:
 
@@ -79,11 +145,11 @@ UPDATE "_session_settings" SET "value" = 'memtx|vinyl' WHERE "name" = 'sql_defau
 pragma sql_default_engine='memtx|vinyl'
 ```
 
-If the first fails, then the second will be executed. When both fails, fail the test.
+If the first fails, then the second will be executed. When both fail, the test fails.
 
-#### Python
+#### Python tests
 
-Files: `<name>.test.py`, `<name>.result` and `<name>.skipcond`(optionaly).
+Files: `<name>.test.py`, `<name>.result` and `<name>.skipcond` (optionally).
 
 Environment:
 
@@ -173,7 +239,7 @@ Tests interact only with `AdminConnection`. Supports some preprocessor functions
 
 **Delimiter example:**
 
-```
+```lua
 env = require('test_run')
 test_run = env.new()
 box.schema.space.create('temp')
@@ -194,7 +260,7 @@ test
 
 **Delimiter result:**
 
-```
+```yaml
 env = require('test_run')
 test_run = env.new()
 box.schema.space.create('temp')