diff --git a/sidecar/src/test/kotlin/dev/sanderling/sidecar/DadbTargetTest.kt b/sidecar/src/test/kotlin/dev/sanderling/sidecar/DadbTargetTest.kt
index 7db71f8..1d1cee5 100644
--- a/sidecar/src/test/kotlin/dev/sanderling/sidecar/DadbTargetTest.kt
+++ b/sidecar/src/test/kotlin/dev/sanderling/sidecar/DadbTargetTest.kt
@@ -2,6 +2,8 @@ package dev.sanderling.sidecar
 
 import org.junit.Test
 import kotlin.test.assertEquals
+import kotlin.test.assertFailsWith
+import kotlin.test.assertTrue
 
 class DadbTargetTest {
 
@@ -22,4 +24,103 @@ class DadbTargetTest {
     @Test fun colonWithNonNumericPortIsAServerSerial() {
         assertEquals(DadbTarget.Server("emulator:5554x"), dadbTargetFor("emulator:5554x"))
     }
+
+    // A serial-addressed device is reached through whichever adb server the
+    // environment names. Ignoring it sends the run to this machine's own
+    // server, where the serial either is missing or, worse, names a different
+    // device that happens to share the emulator numbering.
+    @Test fun adbServerSocketNamesARemoteServer() {
+        assertEquals(
+            AdbServerEndpoint("100.68.126.75", 5037),
+            adbServerEndpoint(
+                env("ADB_SERVER_SOCKET" to "tcp:100.68.126.75:5037"),
+            ),
+        )
+    }
+
+    @Test fun adbServerSocketWithOnlyAPortStaysLocal() {
+        assertEquals(
+            AdbServerEndpoint("localhost", 5038),
+            adbServerEndpoint(env("ADB_SERVER_SOCKET" to "tcp:5038")),
+        )
+    }
+
+    @Test fun androidAdbServerAddressAndPortPairIsHonoured() {
+        assertEquals(
+            AdbServerEndpoint("10.0.0.4", 5040),
+            adbServerEndpoint(
+                env(
+                    "ANDROID_ADB_SERVER_ADDRESS" to "10.0.0.4",
+                    "ANDROID_ADB_SERVER_PORT" to "5040",
+                ),
+            ),
+        )
+    }
+
+    @Test fun adbServerSocketOutranksTheOlderPair() {
+        assertEquals(
+            AdbServerEndpoint("100.68.126.75", 5037),
+            adbServerEndpoint(
+                env(
+                    "ADB_SERVER_SOCKET" to "tcp:100.68.126.75:5037",
+                    "ANDROID_ADB_SERVER_ADDRESS" to "10.0.0.4",
+                    "ANDROID_ADB_SERVER_PORT" to "5040",
+                ),
+            ),
+        )
+    }
+
+    @Test fun unsetEnvironmentKeepsTheLoopbackDefault() {
+        assertEquals(
+            AdbServerEndpoint("localhost", 5037),
+            adbServerEndpoint(env()),
+        )
+        assertEquals(
+            AdbServerEndpoint("localhost", 5037),
+            adbServerEndpoint(env("ADB_SERVER_SOCKET" to "")),
+        )
+    }
+
+    @Test fun eitherHalfOfTheOlderPairAloneKeepsTheOtherDefault() {
+        assertEquals(
+            AdbServerEndpoint("10.0.0.4", 5037),
+            adbServerEndpoint(env("ANDROID_ADB_SERVER_ADDRESS" to "10.0.0.4")),
+        )
+        assertEquals(
+            AdbServerEndpoint("localhost", 5040),
+            adbServerEndpoint(env("ANDROID_ADB_SERVER_PORT" to "5040")),
+        )
+    }
+
+    // A value that cannot be read must stop the run and say which variable
+    // held what. Falling back to loopback would drive this machine's devices
+    // while the operator believes the run is on the remote ones.
+    @Test fun malformedValuesFailNamingTheVariableAndItsContents() {
+        val cases = mapOf(
+            "ADB_SERVER_SOCKET" to listOf(
+                "100.68.126.75:5037",
+                "tcp:100.68.126.75:pear",
+                "tcp:",
+                "tcp::5037",
+                "unix:/tmp/adb",
+                "tcp:100.68.126.75:70000",
+            ),
+            "ANDROID_ADB_SERVER_PORT" to listOf("pear", "0", "-1"),
+        )
+        for ((variable, values) in cases) {
+            for (value in values) {
+                val failure = assertFailsWith<IllegalArgumentException>(value) {
+                    adbServerEndpoint(env(variable to value))
+                }
+                val message = failure.message.orEmpty()
+                assertTrue(message.contains(variable), message)
+                assertTrue(message.contains(value), message)
+            }
+        }
+    }
+}
+
+private fun env(vararg entries: Pair<String, String>): (String) -> String? {
+    val values = entries.toMap()
+    return { values[it] }
 }