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+++ b/tests/README.md
@@ -1,29 +1,98 @@
+Tests
+=====
+
+This directory contains the test cases for AssemblyScript's parser and compiler. A test case
+consists of:
+
+* A test file that is parsed or compiled (.ts)
+* One or multiple automatically generated fixtures generated from the source file
+
+Creating a test:
+
+* Run `npm run clean` to make sure that the sources are tested instead of the distribution
+* Create a new test file (.ts) within the respective directory (see below) that contains your test code
+* Follow the instructions below to generate the first fixture(s)
+* Make sure the fixture(s) contain exactly what you'd expect
+
+Updating a test:
+
+* Run `npm run clean` to make sure that the sources are tested instead of the distribution
+* Make changes to the respective test file (.ts)
+* Follow the instructions below to update the fixture(s)
+* Make sure the fixture(s) contain exactly what you'd expect
+
+See also: [Contribution guidelines](../CONTRIBUTING.md)
+
 Parser
 ------
 
-Tests consist of a test case that is first parsed and then serialized again. The output is then compared to its respective fixture.
+Directory: [tests/parser](./parser)
+
+The test file is parsed while warnings and errors are recorded and re-serialized to a new source
+afterwards. The new source with warnings and errors appended as comments is compared to the fixture.
+
+Running all tests:
 
 ```
-$> npm run test:parser [case name]
+$> npm run test:parser
 ```
 
-To recreate the fixtures:
+Running a specific test only:
+
+```
+$> npm run test:parser -- testNameWithoutTs
+```
+
+To (re-)create all fixtures:
 
 ```
 $>npm run test:parser -- --create
 ```
 
+Note that the parser suite currently can't recreate just a specific fixture.
+
 Compiler
 --------
 
-Tests consist of a test case that is compiled to a module, validated, interpreted, converted to text format and then compared to its respective fixture.
+General directory: [tests/compiler](./compiler)
+Standard library directory: [tests/compiler/std](./compiler/std)
+
+The source file is parsed and compiled to a module, validated, interpreted and the resulting module
+converted to WebAsssembly text format.
+
+The text format output is compared to its fixture and the module interpreted in a WebAssembly VM. To
+assert for runtime conditions, the `assert` builtin can be used. Note that tree-shaking is enabled
+and it might be necessary to export entry points.
+
+Additional fixtures for the optimized module etc. are generated as well but are used for visual
+confirmation only.
+
+Running all tests:
 
 ```
-$> npm run test:compiler [case name]
+$> npm run test:compiler
 ```
 
-To recreate the fixtures:
+Running a specific test only:
 
 ```
-$>npm run test:compiler -- --create
+$> npm run test:compiler -- testNameWithoutTs
 ```
+
+To (re-)create all fixtures:
+
+```
+$> npm run test:compiler -- --create
+```
+
+To (re-)create a specific fixture only:
+
+```
+$> npm run test:compiler -- testNameWithoutTs --create
+```
+
+Other
+-----
+
+Tests in other directories are not run automatically and do not need to be updated. Most of them
+are legacy tests.