testing readme added

Author: Bengt Lofgren

solana/programs/matching-engine/tests/README.md

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+# Matching Engine Tests
+
+## How to read the tests
+
+Each test is found in the `integration_tests.rs` file.
+
+Each test is a function that is annotated with `#[tokio::test]`.
+
+Each test is a test for a specific scenario, and uses the `TestingEngine` to execute a series of instruction triggers.
+
+The `TestingEngine` is initialised with a `TestingContext`. The `TestingContext` holds the solana program test context, the actors, the transfer direction, created vaas, as well as some constants.
+
+The `TestingEngine` is used to execute the instruction triggers in the order they are provided. See the `testing_engine/engine.rs` file for more details.
+
+
+## Integration Tests
+
+### Initialize program
+
+What is expected:
+- Program is initialised
+- Router endpoints are created
+
+### Create fast market order
+
+What is expected:
+- Fast market order account is created
+- Guardian set is created
+- Fast market order is initialised
+
+### Close fast market order
+
+What is expected:
+- Fast market order account is closed
+- Guardian set is closed
+- Close account refund recipient is sent usdc
+
+