[feat] Add basic support for IBM's watsonx code assistant (#2617)

Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

tests/providers/watsonx_code_assistant_spec.lua

@@ -0,0 +1,69 @@
+local busted = require("plenary.busted")
+
+busted.describe("watsonx_code_assistant provider", function()
+  local watsonx_provider
+
+  busted.before_each(function()
+    -- Minimal setup without extensive mocking
+    watsonx_provider = require("avante.providers.watsonx_code_assistant")
+  end)
+
+  busted.describe("basic configuration", function()
+    busted.it("should have required properties", function()
+      assert.is_not_nil(watsonx_provider.api_key_name)
+      assert.equals("WCA_API_KEY", watsonx_provider.api_key_name)
+      assert.is_not_nil(watsonx_provider.role_map)
+      assert.equals("USER", watsonx_provider.role_map.user)
+      assert.equals("ASSISTANT", watsonx_provider.role_map.assistant)
+    end)
+
+    busted.it("should disable streaming", function() assert.is_true(watsonx_provider:is_disable_stream()) end)
+
+    busted.it("should have required functions", function()
+      assert.is_function(watsonx_provider.parse_messages)
+      assert.is_function(watsonx_provider.parse_response_without_stream)
+      assert.is_function(watsonx_provider.parse_curl_args)
+    end)
+  end)
+
+  busted.describe("parse_messages", function()
+    busted.it("should parse messages with correct role mapping", function()
+      ---@type AvantePromptOptions
+      local opts = {
+        system_prompt = "You are a helpful assistant",
+        messages = {
+          { content = "Hello", role = "user" },
+          { content = "Hi there", role = "assistant" },
+        },
+      }
+
+      local result = watsonx_provider:parse_messages(opts)
+
+      assert.is_table(result)
+      assert.equals(3, #result) -- system + 2 messages
+      assert.equals("SYSTEM", result[1].role)
+      assert.equals("You are a helpful assistant", result[1].content)
+      assert.equals("USER", result[2].role)
+      assert.equals("Hello", result[2].content)
+      assert.equals("ASSISTANT", result[3].role)
+      assert.equals("Hi there", result[3].content)
+    end)
+
+    busted.it("should handle WCA_COMMAND system prompt", function()
+      ---@type AvantePromptOptions
+      local opts = {
+        system_prompt = "WCA_COMMAND",
+        messages = {
+          { content = "/document main.py", role = "user" },
+        },
+      }
+
+      local result = watsonx_provider:parse_messages(opts)
+
+      assert.is_table(result)
+      assert.equals(1, #result) -- only user message, no system prompt
+      assert.equals("USER", result[1].role)
+      assert.equals("/document main.py", result[1].content)
+    end)
+  end)
+end)