diff --git a/service/src/test/java/uk/nhs/adaptors/gpc/consumer/sds/SdsClientTest.java b/service/src/test/java/uk/nhs/adaptors/gpc/consumer/sds/SdsClientTest.java
new file mode 100644
index 0000000..044cfba
--- /dev/null
+++ b/service/src/test/java/uk/nhs/adaptors/gpc/consumer/sds/SdsClientTest.java
@@ -0,0 +1,185 @@
+package uk.nhs.adaptors.gpc.consumer.sds;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.Mockito.when;
+
+import org.hl7.fhir.dstu3.model.Bundle;
+import org.hl7.fhir.dstu3.model.Device;
+import org.hl7.fhir.dstu3.model.Endpoint;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+import org.mockito.Mock;
+import org.mockito.junit.jupiter.MockitoExtension;
+import org.springframework.test.util.ReflectionTestUtils;
+import org.springframework.web.reactive.function.client.WebClient;
+
+import ca.uhn.fhir.context.FhirContext;
+import ca.uhn.fhir.parser.IParser;
+import reactor.core.publisher.Mono;
+import reactor.test.StepVerifier;
+import uk.nhs.adaptors.gpc.consumer.sds.builder.SdsRequestBuilder;
+import static org.junit.Assert.assertEquals;
+
+@ExtendWith(MockitoExtension.class)
+class SdsClientTest {
+
+    private static final String FROM_ODS_CODE = "A12345";
+    private static final String CORRELATION_ID = "corr-id-001";
+    private static final String SUPPLIER_ODS_CODE = "SUPPLIER01";
+    private static final String INTERACTION_ID = "urn:nhs:names:services:gpconnect:fhir:operation:gpc.getstructuredrecord-1";
+    private static final String NHS_SPINE_ASID_SYSTEM = "https://fhir.nhs.uk/Id/nhsSpineASID";
+    private static final String NHS_MHS_ID_SYSTEM = "https://fhir.nhs.uk/Id/nhsMHSId";
+    private static final String TEST_ASID = "928940000057";
+    private static final String TEST_MHS_ID = "mhs-id-123";
+    private static final String TEST_ADDRESS = "https://gpc-provider.example.com/fhir";
+
+    private final IParser fhirParser = FhirContext.forDstu3().newJsonParser();
+
+    @Mock
+    private SdsRequestBuilder sdsRequestBuilder;
+
+    @SuppressWarnings("rawtypes")
+    @Mock
+    private WebClient.RequestHeadersSpec deviceRequest;
+
+    @SuppressWarnings("rawtypes")
+    @Mock
+    private WebClient.RequestHeadersSpec endpointRequest;
+
+    @Mock
+    private WebClient.ResponseSpec deviceResponseSpec;
+
+    @Mock
+    private WebClient.ResponseSpec endpointResponseSpec;
+
+    private SdsClient sdsClient;
+
+    @BeforeEach
+    void setUp() {
+        sdsClient = new SdsClient(fhirParser, sdsRequestBuilder);
+        ReflectionTestUtils.setField(sdsClient, "supplierOdsCode", SUPPLIER_ODS_CODE);
+    }
+
+    @Test
+    void When_DeviceBundleContainsSpineAsid_Expect_CallForGetAsidReturnsAsid() {
+        when(sdsRequestBuilder.buildAsDeviceAsidRequest(FROM_ODS_CODE, SUPPLIER_ODS_CODE, INTERACTION_ID, CORRELATION_ID))
+            .thenReturn(deviceRequest);
+        stubDeviceResponse(buildDeviceBundle(TEST_ASID));
+
+        StepVerifier.create(sdsClient.callForGetAsid(INTERACTION_ID, FROM_ODS_CODE, CORRELATION_ID))
+            .assertNext(asid -> assertEquals(TEST_ASID, asid))
+            .verifyComplete();
+    }
+
+    @Test
+    void When_DeviceBundleHasNoEntries_Expect_CallForGetAsidErrors() {
+        when(sdsRequestBuilder.buildAsDeviceAsidRequest(FROM_ODS_CODE, SUPPLIER_ODS_CODE, INTERACTION_ID, CORRELATION_ID))
+            .thenReturn(deviceRequest);
+        stubDeviceResponse(buildEmptyBundle());
+
+        StepVerifier.create(sdsClient.callForGetAsid(INTERACTION_ID, FROM_ODS_CODE, CORRELATION_ID))
+            .expectErrorSatisfies(e -> assertThat(e).isInstanceOf(RuntimeException.class)
+                .hasMessageContaining("SDS returned no result"))
+            .verify();
+    }
+
+    @Test
+    void When_DeviceMissingSpineAsidIdentifier_Expect_CallForGetAsidErrors() {
+        when(sdsRequestBuilder.buildAsDeviceAsidRequest(FROM_ODS_CODE, SUPPLIER_ODS_CODE, INTERACTION_ID, CORRELATION_ID))
+            .thenReturn(deviceRequest);
+        stubDeviceResponse(buildDeviceBundleWithWrongIdentifierSystem());
+
+        StepVerifier.create(sdsClient.callForGetAsid(INTERACTION_ID, FROM_ODS_CODE, CORRELATION_ID))
+            .expectErrorSatisfies(e -> {
+                assertThat(e).isInstanceOf(RuntimeException.class);
+                assertThat(e.getMessage()).contains("Identifier of system");
+            })
+            .verify();
+    }
+
+    @Test
+    void When_BothBundlesAreValid_Expect_CallForGetStructuredRecordReturnsSdsResponseData() {
+        when(sdsRequestBuilder.buildGetStructuredRecordAsDeviceRequest(FROM_ODS_CODE, CORRELATION_ID))
+            .thenReturn(deviceRequest);
+        when(sdsRequestBuilder.buildGetStructuredRecordEndpointRequest(FROM_ODS_CODE, CORRELATION_ID))
+            .thenReturn(endpointRequest);
+        stubDeviceResponse(buildDeviceBundle(TEST_ASID));
+        stubEndpointResponse(buildEndpointBundle(TEST_ADDRESS, TEST_MHS_ID));
+
+        StepVerifier.create(sdsClient.callForGetStructuredRecord(FROM_ODS_CODE, CORRELATION_ID))
+            .assertNext(data -> {
+                assertEquals(TEST_ADDRESS, data.getAddress());
+                assertEquals(TEST_ASID, data.getNhsSpineAsid());
+                assertEquals(TEST_MHS_ID, data.getNhsMhsId());
+            })
+            .verifyComplete();
+    }
+
+    @SuppressWarnings("unchecked")
+    private void stubDeviceResponse(String json) {
+        when(deviceRequest.retrieve()).thenReturn(deviceResponseSpec);
+        when(deviceResponseSpec.bodyToMono(eq(String.class))).thenReturn(Mono.just(json));
+    }
+
+    @SuppressWarnings("unchecked")
+    private void stubEndpointResponse(String json) {
+        when(endpointRequest.retrieve()).thenReturn(endpointResponseSpec);
+        when(endpointResponseSpec.bodyToMono(eq(String.class))).thenReturn(Mono.just(json));
+    }
+
+    private String buildDeviceBundle(String asid) {
+        var bundle = new Bundle();
+        var device = new Device();
+        device.addIdentifier().setSystem(NHS_SPINE_ASID_SYSTEM).setValue(asid);
+        bundle.addEntry().setResource(device);
+        return fhirParser.encodeResourceToString(bundle);
+    }
+
+    private String buildDeviceBundleWithMultipleEntries(String firstAsid, String secondAsid) {
+        var bundle = new Bundle();
+        var device1 = new Device();
+        device1.addIdentifier().setSystem(NHS_SPINE_ASID_SYSTEM).setValue(firstAsid);
+        var device2 = new Device();
+        device2.addIdentifier().setSystem(NHS_SPINE_ASID_SYSTEM).setValue(secondAsid);
+        bundle.addEntry().setResource(device1);
+        bundle.addEntry().setResource(device2);
+        return fhirParser.encodeResourceToString(bundle);
+    }
+
+    private String buildDeviceBundleWithWrongIdentifierSystem() {
+        var bundle = new Bundle();
+        var device = new Device();
+        device.addIdentifier().setSystem("https://fhir.nhs.uk/Id/WRONG_SYSTEM").setValue("some-value");
+        bundle.addEntry().setResource(device);
+        return fhirParser.encodeResourceToString(bundle);
+    }
+
+    private String buildDeviceBundleWithoutIdentifier() {
+        var bundle = new Bundle();
+        bundle.addEntry().setResource(new Device());
+        return fhirParser.encodeResourceToString(bundle);
+    }
+
+    private String buildEndpointBundle(String address, String nhsMhsId) {
+        var bundle = new Bundle();
+        var endpoint = new Endpoint();
+        endpoint.setAddress(address);
+        endpoint.addIdentifier().setSystem(NHS_MHS_ID_SYSTEM).setValue(nhsMhsId);
+        bundle.addEntry().setResource(endpoint);
+        return fhirParser.encodeResourceToString(bundle);
+    }
+
+    private String buildEndpointBundleWithoutMhsId(String address) {
+        var bundle = new Bundle();
+        var endpoint = new Endpoint();
+        endpoint.setAddress(address);
+        bundle.addEntry().setResource(endpoint);
+        return fhirParser.encodeResourceToString(bundle);
+    }
+
+    private String buildEmptyBundle() {
+        return fhirParser.encodeResourceToString(new Bundle());
+    }
+}