Update checkout session flow when state is set. (#13174)

Author: jaynewstrom-stripe

paymentsheet/src/main/java/com/stripe/android/checkout/Checkout.kt

@@ -150,6 +150,7 @@ class Checkout private constructor(
         set(value) {
             ensureNoMutationInFlight()
             internalState = value.internalState
+            _checkoutSession.value = internalState.checkoutSessionResponse.asCheckoutSession()
         }
 
     private val mutex = Mutex()

paymentsheet/src/test/java/com/stripe/android/checkout/CheckoutTest.kt

@@ -776,6 +776,18 @@ class CheckoutTest {
         deferred.await()
     }
 
+    @Test
+    fun `setting state updates checkoutSession flow`() = runCreateWithStateScenario {
+        val initial = checkoutSessionTurbine.awaitItem()
+        assertThat(initial.id).isEqualTo(DEFAULT_CHECKOUT_SESSION_ID)
+
+        val updatedResponse = CheckoutSessionResponseFactory.create(id = "cs_test_updated")
+        checkout.state = CheckoutStateFactory.create(checkoutSessionResponse = updatedResponse)
+
+        val updated = checkoutSessionTurbine.awaitItem()
+        assertThat(updated.id).isEqualTo("cs_test_updated")
+    }
+
     @Test
     fun `mutation returns failure when integrationLaunched is true`() = runCreateWithStateScenario(
         shouldValidateEvents = false,