[test-improver] Improve tests for server http_helpers package

internal/server/http_helpers_test.go

@@ -3,6 +3,7 @@ package server
 import (
 	"bytes"
 	"context"
+	"encoding/json"
 	"io"
 	"net/http"
 	"net/http/httptest"
@@ -730,3 +731,137 @@ func TestLogRuntimeError(t *testing.T) {
 func stringPtr(s string) *string {
 	return &s
 }
+
+// TestWriteErrorResponse verifies that writeErrorResponse writes a JSON error
+// body with "error" and "message" fields and the correct status code and Content-Type.
+func TestWriteErrorResponse(t *testing.T) {
+	tests := []struct {
+		name       string
+		statusCode int
+		code       string
+		message    string
+	}{
+		{
+			name:       "400 bad request",
+			statusCode: http.StatusBadRequest,
+			code:       "bad_request",
+			message:    "the request body is malformed",
+		},
+		{
+			name:       "401 unauthorized",
+			statusCode: http.StatusUnauthorized,
+			code:       "unauthorized",
+			message:    "invalid API key",
+		},
+		{
+			name:       "403 forbidden",
+			statusCode: http.StatusForbidden,
+			code:       "forbidden",
+			message:    "access denied",
+		},
+		{
+			name:       "404 not found",
+			statusCode: http.StatusNotFound,
+			code:       "not_found",
+			message:    "the requested resource does not exist",
+		},
+		{
+			name:       "500 internal server error",
+			statusCode: http.StatusInternalServerError,
+			code:       "internal_error",
+			message:    "an unexpected error occurred",
+		},
+		{
+			name:       "503 service unavailable",
+			statusCode: http.StatusServiceUnavailable,
+			code:       "service_unavailable",
+			message:    "the gateway is shutting down",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			writeErrorResponse(w, tt.statusCode, tt.code, tt.message)
+
+			assert.Equal(t, tt.statusCode, w.Code, "status code should match")
+			assert.Equal(t, "application/json", w.Header().Get("Content-Type"), "Content-Type should be application/json")
+
+			var body map[string]string
+			err := json.NewDecoder(w.Body).Decode(&body)
+			require.NoError(t, err, "response body should be valid JSON")
+			assert.Equal(t, tt.code, body["error"], "response body 'error' field should match code")
+			assert.Equal(t, tt.message, body["message"], "response body 'message' field should match message")
+		})
+	}
+}
+
+// TestRejectRequest verifies that rejectRequest writes the correct HTTP error
+// response and does not panic for a variety of status codes and messages.
+func TestRejectRequest(t *testing.T) {
+	tests := []struct {
+		name           string
+		status         int
+		code           string
+		msg            string
+		logCategory    string
+		runtimeErrType string
+		runtimeDetail  string
+		path           string
+		method         string
+	}{
+		{
+			name:           "401 missing auth header",
+			status:         http.StatusUnauthorized,
+			code:           "unauthorized",
+			msg:            "missing Authorization header",
+			logCategory:    "auth",
+			runtimeErrType: "authentication_failed",
+			runtimeDetail:  "missing_auth_header",
+			path:           "/mcp",
+			method:         "GET",
+		},
+		{
+			name:           "401 invalid api key",
+			status:         http.StatusUnauthorized,
+			code:           "unauthorized",
+			msg:            "invalid API key",
+			logCategory:    "auth",
+			runtimeErrType: "authentication_failed",
+			runtimeDetail:  "invalid_api_key",
+			path:           "/mcp/github",
+			method:         "POST",
+		},
+		{
+			name:           "503 shutdown",
+			status:         http.StatusServiceUnavailable,
+			code:           "service_unavailable",
+			msg:            "Gateway is shutting down",
+			logCategory:    "gateway",
+			runtimeErrType: "shutdown",
+			runtimeDetail:  "shutdown_in_progress",
+			path:           "/mcp",
+			method:         "POST",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			w := httptest.NewRecorder()
+			r := httptest.NewRequest(tt.method, tt.path, nil)
+
+			assert.NotPanics(t, func() {
+				rejectRequest(w, r, tt.status, tt.code, tt.msg, tt.logCategory, tt.runtimeErrType, tt.runtimeDetail)
+			})
+
+			assert.Equal(t, tt.status, w.Code, "status code should match")
+			assert.Equal(t, "application/json", w.Header().Get("Content-Type"), "Content-Type should be application/json")
+
+			var body map[string]string
+			err := json.NewDecoder(w.Body).Decode(&body)
+			require.NoError(t, err, "response body should be valid JSON")
+			assert.Equal(t, tt.code, body["error"], "response body 'error' field should match code")
+			assert.Equal(t, tt.msg, body["message"], "response body 'message' field should match msg")
+		})
+	}
+}