feat(client): override strategy from adapter spec

Allows adapters to implement custom strategies to use in place of
built-in ones such as for nvim-dap.

See #24 (reply in thread)

doc/neotest.txt

@@ -1484,9 +1484,13 @@ Fields~
 {output_stream} `(async fun(): async)` fun(): string Async iterator of process
 output
 
+                                                       *neotest.StrategyContext*
+Fields~
+{position} `(neotest.Position)`
+
                                                               *neotest.Strategy*
 Alias~
-`neotest.Strategy` → `async fun(spec: neotest.RunSpec): neotest.Process`
+`neotest.Strategy` → `async fun(spec: neotest.RunSpec, context: neotest.StrategyContext): neotest.Process`
 
                                                         *neotest.StrategyResult*
 Fields~
@@ -1506,7 +1510,8 @@ Fields~
 {cwd?} `(string)`
 {context?} `(table)` Arbitrary data to preserve state between running and
 result collection
-{strategy?} `(table)` Arguments for strategy
+{strategy?} `(table|neotest.Strategy)` Arguments for strategy or override for
+chosen strategy
 {stream} `(fun(output_stream: fun(): string[]): fun():)` table<string,
 neotest.Result>
 

lua/neotest/client/runner.lua

@@ -102,14 +102,18 @@ end
 ---@param spec neotest.RunSpec
 ---@param adapter neotest.Adapter
 function TestRunner:_run_spec(spec, tree, args, adapter_id, adapter, results_callback)
-  local position = tree:data()
-  spec.strategy =
-    vim.tbl_extend("force", spec.strategy or {}, config.strategies[args.strategy] or {})
+  if type(spec.strategy) == "function" then
+    args = vim.tbl_extend("keep", { strategy = spec.strategy }, args)
+  else
+    spec.strategy =
+      vim.tbl_extend("force", spec.strategy or {}, config.strategies[args.strategy] or {})
+  end
   spec.env = vim.tbl_extend("force", spec.env or {}, args.env or {})
   spec.cwd = args.cwd or spec.cwd
   if vim.tbl_isempty(spec.env or {}) then
     spec.env = nil
   end
+  local position = tree:data()
   local context = {
     position = position,
   }

lua/neotest/types/init.lua

@@ -42,7 +42,7 @@
 ---@field env? table<string, string>
 ---@field cwd? string
 ---@field context? table Arbitrary data to preserve state between running and result collection
----@field strategy? table Arguments for strategy
+---@field strategy? table|neotest.Strategy Arguments for strategy or override for chosen strategy
 ---@field stream fun(output_stream: fun(): string[]): fun(): table<string, neotest.Result>
 
 local M = {}

tests/unit/client/init_spec.lua

@@ -93,7 +93,7 @@ describe("neotest client", function()
           return true
         end,
         output = function()
-          return spec.strategy.output
+          return type(spec.strategy) == "table" and spec.strategy.output or "not_a_file"
         end,
         stop = function()
           exit_future.set()
@@ -111,7 +111,7 @@ describe("neotest client", function()
         end,
         result = function()
           exit_future.wait()
-          return spec.strategy.exit_code
+          return type(spec.strategy) == "table" and spec.strategy.exit_code or 0
         end,
       }
     end
@@ -303,6 +303,31 @@ describe("neotest client", function()
       end
     end)
 
+    a.it("uses spec strategy override", function()
+      local called = nio.control.future()
+      mock_adapter.build_spec = function()
+        return {
+          strategy = function(...)
+            called.set()
+            return mock_strategy(...)
+          end,
+        }
+      end
+      local tree = get_pos(dir)
+      exit_future.set()
+      nio.run(function()
+        client:run_tree(tree, { strategy = mock_strategy })
+      end)
+      called.wait()
+      local adapter_id = client:get_adapters()[1]
+      local results = client:get_results(adapter_id)
+      for _, pos in tree:iter() do
+        if pos.type == "dir" then
+          assert.equal(results[pos.id].status, "failed")
+        end
+      end
+    end)
+
     describe("with unsupported roots", function()
       describe("supporting files", function()
         a.it("breaks up directories to files", function()