add grouping for test listing entries

tests/test_samurai_core_spec.lua

@@ -22,6 +22,14 @@ describe("test-samurai core", function()
     assert.equals("go", runner.name)
   end)
 
+  it("does not fallback to Go runner when no runners are configured", function()
+    test_samurai.setup({ runner_modules = {} })
+    local bufnr = vim.api.nvim_create_buf(false, true)
+    vim.api.nvim_buf_set_name(bufnr, "/tmp/no_runner_test.go")
+    local runner = core.get_runner_for_buf(bufnr)
+    assert.is_nil(runner)
+  end)
+
   it("selects JS jest runner for *.test.ts files", function()
     local bufnr = vim.api.nvim_create_buf(false, true)
     vim.api.nvim_buf_set_name(bufnr, "/tmp/foo.test.ts")