diff --git a/internal/http/at_session_handler_test.go b/internal/http/http_test.go
similarity index 54%
rename from internal/http/at_session_handler_test.go
rename to internal/http/http_test.go
index c99cee7..48d04ca 100644
--- a/internal/http/at_session_handler_test.go
+++ b/internal/http/http_test.go
@@ -1,6 +1,7 @@
 package http
 
 import (
+	"bytes"
 	"context"
 	"errors"
 	"io"
@@ -15,6 +16,16 @@ import (
 	"git.grassecon.net/urdt/ussd/internal/mocks/httpmocks"
 )
 
+// invalidRequestType is a custom type to test invalid request scenarios
+type invalidRequestType struct{}
+
+// errorReader is a helper type that always returns an error when Read is called
+type errorReader struct{}
+
+func (e *errorReader) Read(p []byte) (n int, err error) {
+	return 0, errors.New("read error")
+}
+
 func TestNewATSessionHandler(t *testing.T) {
 	mockHandler := &httpmocks.MockRequestHandler{}
 	ash := NewATSessionHandler(mockHandler)
@@ -90,7 +101,7 @@ func TestATSessionHandler_ServeHTTP(t *testing.T) {
 					return req.FormValue("phoneNumber"), nil
 				}
 				mrp.GetInputFunc = func(rq any) ([]byte, error) {
-					 return nil, errors.New("no input found")
+					return nil, errors.New("no input found")
 				}
 				mh.GetConfigFunc = func() engine.Config { return engine.Config{} }
 				mh.GetRequestParserFunc = func() handlers.RequestParser { return mrp }
@@ -230,3 +241,209 @@ func TestATSessionHandler_Output(t *testing.T) {
 		})
 	}
 }
+
+func TestSessionHandler_ServeHTTP(t *testing.T) {
+	tests := []struct {
+		name           string
+		sessionID      string
+		input          []byte
+		parserErr      error
+		processErr     error
+		outputErr      error
+		resetErr       error
+		expectedStatus int
+	}{
+		{
+			name:           "Success",
+			sessionID:      "123",
+			input:          []byte("test input"),
+			expectedStatus: http.StatusOK,
+		},
+		{
+			name:           "Missing Session ID",
+			sessionID:      "",
+			parserErr:      handlers.ErrSessionMissing,
+			expectedStatus: http.StatusBadRequest,
+		},
+		{
+			name:           "Process Error",
+			sessionID:      "123",
+			input:          []byte("test input"),
+			processErr:     handlers.ErrStorage,
+			expectedStatus: http.StatusInternalServerError,
+		},
+		{
+			name:           "Output Error",
+			sessionID:      "123",
+			input:          []byte("test input"),
+			outputErr:      errors.New("output error"),
+			expectedStatus: http.StatusOK,
+		},
+		{
+			name:           "Reset Error",
+			sessionID:      "123",
+			input:          []byte("test input"),
+			resetErr:       errors.New("reset error"),
+			expectedStatus: http.StatusOK,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			mockRequestParser := &httpmocks.MockRequestParser{
+				GetSessionIdFunc: func(any) (string, error) {
+					return tt.sessionID, tt.parserErr
+				},
+				GetInputFunc: func(any) ([]byte, error) {
+					return tt.input, nil
+				},
+			}
+
+			mockRequestHandler := &httpmocks.MockRequestHandler{
+				ProcessFunc: func(rs handlers.RequestSession) (handlers.RequestSession, error) {
+					return rs, tt.processErr
+				},
+				OutputFunc: func(rs handlers.RequestSession) (handlers.RequestSession, error) {
+					return rs, tt.outputErr
+				},
+				ResetFunc: func(rs handlers.RequestSession) (handlers.RequestSession, error) {
+					return rs, tt.resetErr
+				},
+				GetRequestParserFunc: func() handlers.RequestParser {
+					return mockRequestParser
+				},
+				GetConfigFunc: func() engine.Config {
+					return engine.Config{}
+				},
+			}
+
+			sessionHandler := ToSessionHandler(mockRequestHandler)
+
+			req := httptest.NewRequest(http.MethodPost, "/", bytes.NewBuffer(tt.input))
+			req.Header.Set("X-Vise-Session", tt.sessionID)
+
+			rr := httptest.NewRecorder()
+
+			sessionHandler.ServeHTTP(rr, req)
+
+			if status := rr.Code; status != tt.expectedStatus {
+				t.Errorf("handler returned wrong status code: got %v want %v",
+					status, tt.expectedStatus)
+			}
+		})
+	}
+}
+
+func TestSessionHandler_writeError(t *testing.T) {
+	handler := &SessionHandler{}
+	mockWriter := &httpmocks.MockWriter{}
+	err := errors.New("test error")
+
+	handler.writeError(mockWriter, http.StatusBadRequest, err)
+
+	if mockWriter.WrittenString != "" {
+		t.Errorf("Expected empty body, got %s", mockWriter.WrittenString)
+	}
+}
+
+func TestDefaultRequestParser_GetSessionId(t *testing.T) {
+	tests := []struct {
+		name          string
+		request       any
+		expectedID    string
+		expectedError error
+	}{
+		{
+			name: "Valid Session ID",
+			request: func() *http.Request {
+				req := httptest.NewRequest(http.MethodPost, "/", nil)
+				req.Header.Set("X-Vise-Session", "123456")
+				return req
+			}(),
+			expectedID:    "123456",
+			expectedError: nil,
+		},
+		{
+			name:          "Missing Session ID",
+			request:       httptest.NewRequest(http.MethodPost, "/", nil),
+			expectedID:    "",
+			expectedError: handlers.ErrSessionMissing,
+		},
+		{
+			name:          "Invalid Request Type",
+			request:       invalidRequestType{},
+			expectedID:    "",
+			expectedError: handlers.ErrInvalidRequest,
+		},
+	}
+
+	parser := &DefaultRequestParser{}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			id, err := parser.GetSessionId(tt.request)
+
+			if id != tt.expectedID {
+				t.Errorf("Expected session ID %s, got %s", tt.expectedID, id)
+			}
+
+			if err != tt.expectedError {
+				t.Errorf("Expected error %v, got %v", tt.expectedError, err)
+			}
+		})
+	}
+}
+
+func TestDefaultRequestParser_GetInput(t *testing.T) {
+	tests := []struct {
+		name          string
+		request       any
+		expectedInput []byte
+		expectedError error
+	}{
+		{
+			name: "Valid Input",
+			request: func() *http.Request {
+				return httptest.NewRequest(http.MethodPost, "/", bytes.NewBufferString("test input"))
+			}(),
+			expectedInput: []byte("test input"),
+			expectedError: nil,
+		},
+		{
+			name:          "Empty Input",
+			request:       httptest.NewRequest(http.MethodPost, "/", nil),
+			expectedInput: []byte{},
+			expectedError: nil,
+		},
+		{
+			name:          "Invalid Request Type",
+			request:       invalidRequestType{},
+			expectedInput: nil,
+			expectedError: handlers.ErrInvalidRequest,
+		},
+		{
+			name: "Read Error",
+			request: func() *http.Request {
+				return httptest.NewRequest(http.MethodPost, "/", &errorReader{})
+			}(),
+			expectedInput: nil,
+			expectedError: errors.New("read error"),
+		},
+	}
+
+	parser := &DefaultRequestParser{}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			input, err := parser.GetInput(tt.request)
+
+			if !bytes.Equal(input, tt.expectedInput) {
+				t.Errorf("Expected input %s, got %s", tt.expectedInput, input)
+			}
+
+			if err != tt.expectedError && (err == nil || err.Error() != tt.expectedError.Error()) {
+				t.Errorf("Expected error %v, got %v", tt.expectedError, err)
+			}
+		})
+	}
+}