Add integration test framework

EIP-010-integration-test-framework.md

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+#  Integration test framework
+
+## Purpose
+
+Extism have many language's SDk and PDK, which is excellent! but we're lack of tests to make sure all SDK and PDK are working expectedly.
+
+for example: we made a change to GO-PDK, tested with GO-SDK, Rust-SDK but breaks JS-SDK.
+
+So we need a integration test framework to test over all SDK/PDK permutations.
+
+## Solution
+
+### Key concepts
+
+#### TestTarget
+Represents the test running environment,  
+Includes env(different toolchains), PDK(and/or version), SDK(and/or version).
+
+example:
+```yaml
+env:
+  - tiny-go=23.0.1
+sdk: js-sdk=2.0.0-rc
+pdk: go-pdk=latest
+```
+
+env feature is optional.
+
+#### TestSuite
+Represents a group of TestCases with options.
+
+options:
+  - targets: target matchers, use to skip unimplemented/unsupported target or env
+
+#### TestCase
+- inside a TestSuite
+- have an expected output to validate
+
+
+### Workflow
+
+1. design TestSuite and TestCases for ALL SDK/PDK
+2. implement TestSuites
+    - each PDK/SDK to test should implement the TestSuite code, follow the expected output
+    - store in a standardlong repo?
+3. define TestTargets(optional)
+    - can define additaional TestTargets to run test suites
+4. trigger runner by new version released or by manual
+
+
+### Runflow
+Use your favorite build tools to implement, recomment base on Docker.  
+
+1. scan TestSuite and TestCases to generate inital TestTargets
+2. mix inital TestTargets with additaional TestTargets
+3. prepare environment
+    - compile wasm binaries with specified toolchain and PDK
+    - prepare SDKs
+4. run all TestTargets
+5. check output is expected and generate test report
+
+
+## Considerations
+- need a Runner to run SDK code and PDK binary, also can be used to benchmark
+- better not use assert library to check output, just compare output itself to keep it simple.
+- TestSuite versioning, consider SDK/PDK may introduce breaking change
+- prevent overcomplicated