[tests] add test framework new design RFC

Signed-off-by: Avimitin <[email protected]>

tests/designs.md

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+---
+start-date: 2025-01-18
+author: Avimitin
+---
+
+# Summary
+[summary]: #summary
+
+This document is here to describe the new Nix build system designs for T1 test
+cases category. It aims to provide a tests framework that integrate all the T1
+compiler, emulator, linker script...etc to one environment, and any developer,
+even those who doesn't know how Nix works can easily get their code working on
+T1 emulator.
+
+# Motivation
+[motivation]: #motivation
+
+T1 RTLs is now stable and the needs for more contributor to support more
+variety of code cases is increasing. Our current Nix build system is design for
+internal usage. For software developer, they probably wants a project that
+works like Spike or QEMU which contains CLI toolchains that are easy to use and
+doesn't have the requirement of code and framework design to run their code.
+Also the CLI interface should be simple because most of them hate reading manual.
+Our current workflow doesn't well support that.
+
+Besides, although our Nix framework does have scalability, it contains too much
+tech debt and even the best Nix code writer in our team will need to spend some
+time to understand the complex build system design. We need to modify the
+framework to be more straightforward, before we can't handle it.
+
+# Detailed design
+[design]: #detailed-design
+
+According the motivation part, we have two goals to achieve:
+
+* Outside contributors can easily run and integrate their application to T1 project.
+* A new scalable test framework that are easy to maintain.
+
+## Framework Designs
+
+### Machine requirement
+
+As T1 contains multiple TOPs and configs to support, the code may or may not
+runs on some of the combilation. For example, codes that contains floating
+number calculation can't runs on config without Zve32f extension, and some
+codes might required larger VLEN to have better performance. We should give
+user a fatal error when they use incompatible config to run their code and a
+warning when they run with config that doesn't support the application quite
+well.
+
+The old T1 test framework did support this feature. Each test case optionally
+provides a `features-required` field to specify what config should be provided.
+The top config level will provides current selection detail, and a middleware will
+check if the requirement match the current selection.
+
+Nixpkgs also contains similar logic for target host check:
+derivations declared their target host requirement by field `meta.platform`,
+And the Nixpkgs library provide a function `availableOn`
+
+# Examples and Interactions
+[examples-and-interactions]: #examples-and-interactions
+
+This section illustrates the detailed design.
+This section should clarify all confusion the reader has from the previous sections.
+It is especially important to counterbalance the desired terseness of the detailed design;
+if you feel your detailed design is rudely short, consider making this section longer instead.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+What are the disadvantages of doing this?
+
+# Alternatives
+[alternatives]: #alternatives
+
+What other designs have been considered? What is the impact of not doing this?
+For each design decision made, discuss possible alternatives and compare them to the chosen solution.
+The reader should be convinced that this is indeed the best possible solution for the problem at hand.
+
+# Prior art
+[prior-art]: #prior-art
+
+You are unlikely to be the first one to tackle this problem.
+Try to dig up earlier discussions around the topic or prior attempts at improving things.
+Summarize, discuss what was good or bad, and compare to the current proposal.
+If applicable, have a look at what other projects and communities are doing.
+You may also discuss related work here, although some of that might be better located in other sections.
+
+# Unresolved questions
+[unresolved]: #unresolved-questions
+
+What parts of the design are still TBD or unknowns?
+
+# Future work
+[future]: #future-work
+
+What future work, if any, would be implied or impacted by this feature without being directly part of the work?