cpsir unittests: move all unittests into individual files and test runners.

tests/compiler/dart2js/cps_ir/README.md

+# CPS IR unit tests
+
+This folder contains unit tests of the CPS IR. These tests run the compiler with
+the cps IR and check for the output of a specific function (typically main).
+
+To make our lives easier, most files here are autogenerated. You should never
+have to edit a file under `expected/` or any file with an `AUTOGENERATED` header
+(including the `_test.dart` files).
+
+See instructions below to add or update tests.
+
+### Adding a new test
+
+Every test has 3 files: an input file, a test runner file, and an expectation
+file. The last two are auto-generated.  Here is how:
+
+* add a file under `input/` with a unique name, such as `foo_bar.dart`. Do not
+  include `_test` in the name of this file, otherwise the test framework will
+  think this test needs to be run directly in the vm and in a browser, that's
+  not our goal.
+
+* generate the corresponding test file, by running the `up_to_date_test.dart`
+  passing `update` as an argument:
+
+```bash
+dart tests/compiler/dart2js/cps_ir/up_to_date_test.dart update
+```
+
+  This will generate a file `foo_bar_test.dart` on this folder.
+
+* generate the expectations of the test file by running the generated test file
+  with `update` as an argument:
+
+```bash
+dart --package-root=out/ReleaseX64/packages tests/compiler/dart2js/cps_ir/foo_bar_test.dart update
+```
+
+  This will generate a file `expected/foo_bar.js` with the expected output.
+
+### Updating a single test expectation
+
+To update the expectations of a test, simply regenerate it by running the test
+file with `update` as an argument:
+
+```bash
+dart --package-root=out/ReleaseX64/packages tests/compiler/dart2js/cps_ir/foo_bar_test.dart update
+```
+
+This will override the file `expected/foo_bar.js` file with the new output.
+
+If a test fails because the expectations are out of date, you'll see this
+suggestion in the failure message too.
+
+### Updating all test expectations
+
+For convenience, we also provide a script to update all expectations at once.
+
+```bash
+dart --package-root=out/ReleaseX64/packages tests/compiler/dart2js/cps_ir/update_all.dart
+```
+
+It is equivalent to update each test individually. This script can be handy when
+making cross-cutting changes that affect the output of most tests.