diff --git a/image_test.go b/image_test.go
index 644005515..bb9a086fd 100644
--- a/image_test.go
+++ b/image_test.go
@@ -4,6 +4,7 @@ import (
 	utils "github.com/sashabaranov/go-openai/internal"
 	"github.com/sashabaranov/go-openai/internal/test/checks"
 
+	"bytes"
 	"context"
 	"fmt"
 	"io"
@@ -156,3 +157,52 @@ func TestVariImageFormBuilderFailures(t *testing.T) {
 	_, err = client.CreateVariImage(ctx, req)
 	checks.ErrorIs(t, err, mockFailedErr, "CreateImage should return error if form builder fails")
 }
+
+type testNamedReader struct{ io.Reader }
+
+func (testNamedReader) Name() string { return "named.txt" }
+
+func TestWrapReader(t *testing.T) {
+	r := bytes.NewBufferString("data")
+	wrapped := WrapReader(r, "file.png", "image/png")
+	f, ok := wrapped.(interface {
+		Name() string
+		ContentType() string
+	})
+	if !ok {
+		t.Fatal("wrapped reader missing Name or ContentType")
+	}
+	if f.Name() != "file.png" {
+		t.Fatalf("expected name file.png, got %s", f.Name())
+	}
+	if f.ContentType() != "image/png" {
+		t.Fatalf("expected content type image/png, got %s", f.ContentType())
+	}
+
+	// test name from underlying reader
+	nr := testNamedReader{Reader: bytes.NewBufferString("d")}
+	wrapped = WrapReader(nr, "", "text/plain")
+	f, ok = wrapped.(interface {
+		Name() string
+		ContentType() string
+	})
+	if !ok {
+		t.Fatal("wrapped named reader missing Name or ContentType")
+	}
+	if f.Name() != "named.txt" {
+		t.Fatalf("expected name named.txt, got %s", f.Name())
+	}
+	if f.ContentType() != "text/plain" {
+		t.Fatalf("expected content type text/plain, got %s", f.ContentType())
+	}
+
+	// no name provided
+	wrapped = WrapReader(bytes.NewBuffer(nil), "", "")
+	f2, ok := wrapped.(interface{ Name() string })
+	if !ok {
+		t.Fatal("wrapped anonymous reader missing Name")
+	}
+	if f2.Name() != "" {
+		t.Fatalf("expected empty name, got %s", f2.Name())
+	}
+}
diff --git a/internal/error_accumulator_test.go b/internal/error_accumulator_test.go
index 3fa9d7714..f6c226c5e 100644
--- a/internal/error_accumulator_test.go
+++ b/internal/error_accumulator_test.go
@@ -4,6 +4,7 @@ import (
 	"testing"
 
 	openai "github.com/sashabaranov/go-openai/internal"
+	"github.com/sashabaranov/go-openai/internal/test"
 	"github.com/sashabaranov/go-openai/internal/test/checks"
 )
 
@@ -30,3 +31,9 @@ func TestDefaultErrorAccumulator_EmptyBuffer(t *testing.T) {
 		t.Fatal("Buffer should be empty initially")
 	}
 }
+
+func TestDefaultErrorAccumulator_WriteError(t *testing.T) {
+	ea := &openai.DefaultErrorAccumulator{Buffer: &test.FailingErrorBuffer{}}
+	err := ea.Write([]byte("fail"))
+	checks.ErrorIs(t, err, test.ErrTestErrorAccumulatorWriteFailed, "Write should propagate buffer errors")
+}
diff --git a/internal/form_builder_test.go b/internal/form_builder_test.go
index ddd6b8448..1cc82ab8a 100644
--- a/internal/form_builder_test.go
+++ b/internal/form_builder_test.go
@@ -161,3 +161,17 @@ func TestWriteField(t *testing.T) {
 		checks.NoError(t, err, "should write field without error")
 	})
 }
+
+func TestCreateFormFile(t *testing.T) {
+	buf := &bytes.Buffer{}
+	builder := NewFormBuilder(buf)
+
+	err := builder.createFormFile("file", bytes.NewBufferString("data"), "")
+	if err == nil {
+		t.Fatal("expected error for empty filename")
+	}
+
+	builder = NewFormBuilder(&failingWriter{})
+	err = builder.createFormFile("file", bytes.NewBufferString("data"), "name")
+	checks.ErrorIs(t, err, errMockFailingWriterError, "should propagate writer error")
+}
diff --git a/internal/request_builder_test.go b/internal/request_builder_test.go
index e26022a6b..1561b87fb 100644
--- a/internal/request_builder_test.go
+++ b/internal/request_builder_test.go
@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"errors"
+	"io"
 	"net/http"
 	"reflect"
 	"testing"
@@ -59,3 +60,29 @@ func TestRequestBuilderReturnsRequestWhenRequestOfArgsIsNil(t *testing.T) {
 		t.Errorf("Build() got = %v, want %v", got, want)
 	}
 }
+
+func TestRequestBuilderWithReaderBodyAndHeader(t *testing.T) {
+	b := NewRequestBuilder()
+	ctx := context.Background()
+	method := http.MethodPost
+	url := "/reader"
+	bodyContent := "hello"
+	body := bytes.NewBufferString(bodyContent)
+	header := http.Header{"X-Test": []string{"val"}}
+
+	req, err := b.Build(ctx, method, url, body, header)
+	if err != nil {
+		t.Fatalf("Build returned error: %v", err)
+	}
+
+	gotBody, err := io.ReadAll(req.Body)
+	if err != nil {
+		t.Fatalf("cannot read body: %v", err)
+	}
+	if string(gotBody) != bodyContent {
+		t.Fatalf("expected body %q, got %q", bodyContent, string(gotBody))
+	}
+	if req.Header.Get("X-Test") != "val" {
+		t.Fatalf("expected header set to val, got %q", req.Header.Get("X-Test"))
+	}
+}