Added the exact token count for Anthropic and OpenAI (#1004)

app/Tests/Provider/ResponsesUsageTests.cs

@@ -0,0 +1,95 @@
+using System.Text.Json;
+
+using AIStudio.Provider;
+using AIStudio.Provider.OpenAI;
+
+namespace AIStudio.Tests.Provider;
+
+/// <summary>
+/// Checks that what OpenAI says a Responses API call cost is read off the completed event, and only
+/// believed when it describes the request.
+/// </summary>
+/// <remarks>
+/// The completed event states the input of the whole response. That is the request as it was sent,
+/// unless OpenAI ran a hosted tool along the way: what such a tool found is charged as input of the
+/// same response, and no later request carries it. Believe the number then, and a single web search
+/// makes the chat look several times as large as it is.
+/// </remarks>
+[TestFixture]
+public sealed class ResponsesUsageTests
+{
+    private const string COMPLETED_PREFIX = """{"type":"response.completed","sequence_number":42,"response":{"id":"resp_1","object":"response","status":"completed","model":"gpt-5","output":[""";
+    private const string MESSAGE_ITEM = """{"id":"msg_1","type":"message","status":"completed","role":"assistant","content":[{"type":"output_text","text":"Hi there!","annotations":[]}]}""";
+    private const string USAGE_SUFFIX = ""","usage":{"input_tokens":2006,"input_tokens_details":{"cached_tokens":1920},"output_tokens":300,"output_tokens_details":{"reasoning_tokens":120},"total_tokens":2306}}}""";
+
+    [Test]
+    public void TheCompletedEventStatesWhatTheRequestCarried()
+    {
+        //
+        // The cached tokens are a share of the input tokens, not an addition to them: the request
+        // carried 2,006 tokens, 1,920 of which came out of the cache.
+        //
+        var line = Read(COMPLETED_PREFIX + MESSAGE_ITEM + "]" + USAGE_SUFFIX);
+
+        Assert.Multiple(() =>
+        {
+            Assert.That(line.GetUsage().IsKnown, Is.True);
+            Assert.That(line.GetUsage().PromptTokens, Is.EqualTo(2006));
+        });
+    }
+
+    [Test]
+    public void ReasoningAndFunctionCallsLeaveTheInputAlone()
+    {
+        //
+        // Both are output the model wrote itself. Neither makes OpenAI add anything to the input,
+        // and the function call's result comes back in the next request, which states its own.
+        //
+        var line = Read(COMPLETED_PREFIX +
+                        """{"type":"reasoning","id":"rs_1","summary":[],"encrypted_content":"gAAAAAB0aXRs"},""" +
+                        """{"type":"function_call","call_id":"call_1","name":"web_search","arguments":"{\"query\":\"weather\"}"}""" +
+                        "]" + USAGE_SUFFIX);
+
+        Assert.That(line.GetUsage().PromptTokens, Is.EqualTo(2006));
+    }
+
+    [Test]
+    public void AHostedWebSearchStatesNothing()
+    {
+        //
+        // OpenAI searched on its own, and what it found is part of the input tokens. The next
+        // request carries none of it.
+        //
+        var line = Read(COMPLETED_PREFIX +
+                        """{"type":"web_search_call","id":"ws_1","status":"completed","action":{"type":"search","query":"weather"}},""" +
+                        MESSAGE_ITEM +
+                        "]" + USAGE_SUFFIX);
+
+        Assert.That(line.GetUsage().IsKnown, Is.False);
+    }
+
+    [Test]
+    public void AnOutputItemNobodyKnowsStatesNothing()
+    {
+        //
+        // A hosted tool OpenAI adds later is treated like the web search until somebody checked
+        // what it does to the input.
+        //
+        var line = Read(COMPLETED_PREFIX +
+                        """{"type":"future_tool_call","id":"ft_1","status":"completed"},""" +
+                        MESSAGE_ITEM +
+                        "]" + USAGE_SUFFIX);
+
+        Assert.That(line.GetUsage().IsKnown, Is.False);
+    }
+
+    [Test]
+    public void ACompletedEventWithoutAUsageStatesNothing()
+    {
+        var line = Read(COMPLETED_PREFIX + MESSAGE_ITEM + "]}}");
+
+        Assert.That(line.GetUsage().IsKnown, Is.False);
+    }
+
+    private static ResponsesCompletedStreamLine Read(string data) => JsonSerializer.Deserialize<ResponsesCompletedStreamLine>(data, ProviderJsonOptions.OPTIONS)!;
+}