docs: enhance the Logger middleware document.

lib/tesla/middleware/logger.ex

@@ -54,7 +54,7 @@ defmodule Tesla.Middleware.Logger do
 
   ## Options
 
-  - `:log_level` - custom function for calculating log level (see below)
+  - `:log_level` - custom option for calculating log level when get `{:ok, response}` after call.(see below)
   - `:filter_headers` - sanitizes sensitive headers before logging in debug mode (see below)
   - `:debug` - show detailed request/response logging
 
@@ -81,7 +81,7 @@ defmodule Tesla.Middleware.Logger do
   - `:warn` - for 3xx responses
   - `:info` - for 2xx responses
 
-  You can customize this setting by providing your own `log_level/1` function:
+  You can customize this setting by providing your own `log_level/1` function when you get `{:ok, response}` after call:
 
   ```
   defmodule MyClient do
@@ -98,6 +98,19 @@ defmodule Tesla.Middleware.Logger do
   end
   ```
 
+  In some cases, you can also provide the build-in level directly for customization:
+
+  ```
+  defmodule MyClient do
+    use Tesla
+    plug Tesla.Middleware.Logger, log_level: :debug
+  end
+  ```
+
+  NOTE:
+  - **If you get `{:error, whatever}`, the log_level will be `:error`.**
+  - You can get more log level information from [`Logger.Handler`](https://github.com/elixir-lang/elixir/blob/main/lib/logger/lib/logger/handler.ex)
+
   ## Logger Debug output
 
   When the Elixir Logger log level is set to `:debug`

test/tesla/middleware/logger_test.exs

@@ -167,6 +167,9 @@ defmodule Tesla.Middleware.LoggerTest do
 
           "/ok" ->
             {:ok, %{env | status: 200, body: "ok"}}
+
+          "/specific_error" ->
+            {:error, "a specific error"}
         end
       end
     end
@@ -185,6 +188,55 @@ defmodule Tesla.Middleware.LoggerTest do
       log = capture_log(fn -> ClientWithLogLevel.get("/ok") end)
       assert log =~ "[info] GET /ok -> 200"
     end
+
+    test "specific error" do
+      log = capture_log(fn -> ClientWithLogLevel.get("/specific_error") end)
+      assert log =~ "[error] GET /specific_error -> error"
+    end
+  end
+
+  describe "with log_level which provided build-in level directly" do
+    defmodule ClientWithLogLevelDirectly do
+      use Tesla
+
+      plug Tesla.Middleware.Logger, log_level: :error
+
+      adapter fn env ->
+        case env.url do
+          "/bad-request" ->
+            {:ok, %{env | status: 400, body: "bad request"}}
+
+          "/not-found" ->
+            {:ok, %{env | status: 404, body: "not found"}}
+
+          "/ok" ->
+            {:ok, %{env | status: 200, body: "ok"}}
+
+          "/specific_error" ->
+            {:error, "a specific error"}
+        end
+      end
+    end
+
+    test "not found" do
+      log = capture_log(fn -> ClientWithLogLevelDirectly.get("/not-found") end)
+      assert log =~ "[error] GET /not-found -> 404"
+    end
+
+    test "bad request" do
+      log = capture_log(fn -> ClientWithLogLevelDirectly.get("/bad-request") end)
+      assert log =~ "[error] GET /bad-request -> 400"
+    end
+
+    test "ok" do
+      log = capture_log(fn -> ClientWithLogLevelDirectly.get("/ok") end)
+      assert log =~ "[error] GET /ok -> 200"
+    end
+
+    test "specific error" do
+      log = capture_log(fn -> ClientWithLogLevelDirectly.get("/specific_error") end)
+      assert log =~ "[error] GET /specific_error -> error"
+    end
   end
 
   describe "with filter_headers" do