diff --git a/internal/pkg/errors/errors_test.go b/internal/pkg/errors/errors_test.go
index 25e6290..67a6433 100644
--- a/internal/pkg/errors/errors_test.go
+++ b/internal/pkg/errors/errors_test.go
@@ -181,3 +181,52 @@ func TestToHTTP_MetadataDeepCopy(t *testing.T) {
 	appErr.Metadata["k"] = "changed-again"
 	require.Equal(t, "v", body.Metadata["k"])
 }
+
+func TestHTTPStatusErrorFunctions(t *testing.T) {
+	tests := []struct {
+		name     string
+		createFn func(string, string) *ApplicationError
+		isFn     func(error) bool
+		code     int
+	}{
+		{"BadRequest", BadRequest, IsBadRequest, http.StatusBadRequest},
+		{"TooManyRequests", TooManyRequests, IsTooManyRequests, http.StatusTooManyRequests},
+		{"Unauthorized", Unauthorized, IsUnauthorized, http.StatusUnauthorized},
+		{"Forbidden", Forbidden, IsForbidden, http.StatusForbidden},
+		{"NotFound", NotFound, IsNotFound, http.StatusNotFound},
+		{"Conflict", Conflict, IsConflict, http.StatusConflict},
+		{"InternalServer", InternalServer, IsInternalServer, http.StatusInternalServerError},
+		{"ServiceUnavailable", ServiceUnavailable, IsServiceUnavailable, http.StatusServiceUnavailable},
+		{"GatewayTimeout", GatewayTimeout, IsGatewayTimeout, http.StatusGatewayTimeout},
+		{"ClientClosed", ClientClosed, IsClientClosed, 499},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name+"_create", func(t *testing.T) {
+			err := tt.createFn("REASON", "message")
+			require.Equal(t, int32(tt.code), err.Code)
+			require.Equal(t, "REASON", err.Reason)
+			require.Equal(t, "message", err.Message)
+		})
+
+		t.Run(tt.name+"_is_true", func(t *testing.T) {
+			err := New(tt.code, "ANY", "test")
+			require.True(t, tt.isFn(err))
+		})
+
+		t.Run(tt.name+"_is_false", func(t *testing.T) {
+			err := New(tt.code+1, "ANY", "test")
+			require.False(t, tt.isFn(err))
+		})
+
+		t.Run(tt.name+"_is_nil", func(t *testing.T) {
+			require.False(t, tt.isFn(nil))
+		})
+	}
+}
+
+func TestToHTTP_NonApplicationError(t *testing.T) {
+	code, body := ToHTTP(stderrors.New("plain error"))
+	require.Equal(t, http.StatusInternalServerError, code)
+	require.Equal(t, int32(UnknownCode), body.Code)
+}
diff --git a/internal/pkg/googleapi/status_test.go b/internal/pkg/googleapi/status_test.go
new file mode 100644
index 0000000..8f2eb1b
--- /dev/null
+++ b/internal/pkg/googleapi/status_test.go
@@ -0,0 +1,40 @@
+package googleapi
+
+import (
+	"net/http"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestHTTPStatusToGoogleStatus(t *testing.T) {
+	tests := []struct {
+		name   string
+		status int
+		want   string
+	}{
+		{"bad_request_400", http.StatusBadRequest, "INVALID_ARGUMENT"},
+		{"unauthorized_401", http.StatusUnauthorized, "UNAUTHENTICATED"},
+		{"forbidden_403", http.StatusForbidden, "PERMISSION_DENIED"},
+		{"not_found_404", http.StatusNotFound, "NOT_FOUND"},
+		{"too_many_requests_429", http.StatusTooManyRequests, "RESOURCE_EXHAUSTED"},
+		{"internal_server_500", http.StatusInternalServerError, "INTERNAL"},
+		{"bad_gateway_502", http.StatusBadGateway, "INTERNAL"},
+		{"service_unavailable_503", http.StatusServiceUnavailable, "INTERNAL"},
+		{"ok_200", http.StatusOK, "UNKNOWN"},
+		{"created_201", http.StatusCreated, "UNKNOWN"},
+		{"accepted_202", http.StatusAccepted, "UNKNOWN"},
+		{"no_content_204", http.StatusNoContent, "UNKNOWN"},
+		{"bad_request_boundary", 400, "INVALID_ARGUMENT"},
+		{"server_error_boundary", 500, "INTERNAL"},
+		{"custom_4xx", 418, "UNKNOWN"},
+		{"custom_5xx", 599, "INTERNAL"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := HTTPStatusToGoogleStatus(tt.status)
+			require.Equal(t, tt.want, got)
+		})
+	}
+}
diff --git a/internal/pkg/httputil/body_test.go b/internal/pkg/httputil/body_test.go
new file mode 100644
index 0000000..f3782c6
--- /dev/null
+++ b/internal/pkg/httputil/body_test.go
@@ -0,0 +1,101 @@
+package httputil
+
+import (
+	"bytes"
+	"io"
+	"net/http"
+	"strings"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestReadRequestBodyWithPrealloc(t *testing.T) {
+	tests := []struct {
+		name          string
+		req           *http.Request
+		wantBody      []byte
+		wantErr       bool
+		wantNilResult bool
+	}{
+		{
+			name:          "nil_request",
+			req:           nil,
+			wantNilResult: true,
+		},
+		{
+			name: "nil_body",
+			req: &http.Request{
+				Body: nil,
+			},
+			wantNilResult: true,
+		},
+		{
+			name: "empty_body",
+			req: &http.Request{
+				Body:       http.NoBody,
+				ContentLength: 0,
+			},
+			wantBody: []byte{},
+		},
+		{
+			name: "small_body_content_length_100",
+			req: func() *http.Request {
+				body := strings.NewReader("small body content")
+				return &http.Request{
+					Body:          io.NopCloser(body),
+					ContentLength: 100,
+				}
+			}(),
+			wantBody: []byte("small body content"),
+		},
+		{
+			name: "large_body",
+			req: func() *http.Request {
+				data := bytes.Repeat([]byte("x"), 2000)
+				return &http.Request{
+					Body:          io.NopCloser(bytes.NewReader(data)),
+					ContentLength: 2000,
+				}
+			}(),
+			wantBody: bytes.Repeat([]byte("x"), 2000),
+		},
+		{
+			name: "very_large_body",
+			req: func() *http.Request {
+				data := bytes.Repeat([]byte("y"), 2<<20+1000) // > 2MB
+				return &http.Request{
+					Body:          io.NopCloser(bytes.NewReader(data)),
+					ContentLength: int64(2<<20 + 1000),
+				}
+			}(),
+			wantBody: bytes.Repeat([]byte("y"), 2<<20+1000),
+		},
+		{
+			name: "chunked_transfer_encoding",
+			req: func() *http.Request {
+				return &http.Request{
+					Body:          io.NopCloser(strings.NewReader("chunked data")),
+					ContentLength: -1,
+				}
+			}(),
+			wantBody: []byte("chunked data"),
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := ReadRequestBodyWithPrealloc(tt.req)
+			if tt.wantErr {
+				require.Error(t, err)
+				return
+			}
+			require.NoError(t, err)
+			if tt.wantNilResult {
+				require.Nil(t, got)
+			} else {
+				require.Equal(t, tt.wantBody, got)
+			}
+		})
+	}
+}