Environment provider should allow clients to set environment values

lib/src/main/java/com/telemetrydeck/sdk/EnvironmentMetadataProvider.kt

@@ -67,7 +67,9 @@ class EnvironmentMetadataProvider : TelemetryProvider {
     ): Map<String, String> {
         val signalPayload = additionalPayload.toMutableMap()
         for (item in metadata) {
-            signalPayload[item.key] = item.value
+            if (!signalPayload.containsKey(item.key)) {
+                signalPayload[item.key] = item.value
+            }
         }
         return signalPayload
     }

lib/src/test/java/com/telemetrydeck/sdk/EnvironmentMetadataProviderTest.kt

@@ -0,0 +1,40 @@
+package com.telemetrydeck.sdk
+
+import androidx.arch.core.executor.testing.InstantTaskExecutorRule
+import org.junit.Assert
+import org.junit.Rule
+import org.junit.Test
+import java.util.UUID
+
+class EnvironmentMetadataProviderTest {
+    @get:Rule
+    val instantTaskExecutorRule = InstantTaskExecutorRule()
+
+    @Test
+    fun environmentMetadataProvider_sets_client_version() {
+        val appID = "32CB6574-6732-4238-879F-582FEBEB6536"
+        val config = TelemetryManagerConfiguration(appID)
+        val manager =  TelemetryManager.Builder().configuration(config).build(null)
+
+        manager.queue("type", "clientUser", emptyMap())
+
+        val queuedSignal = manager.cache?.empty()?.first()
+
+        Assert.assertNotNull(queuedSignal)
+        Assert.assertEquals(queuedSignal?.payload?.contains("telemetryClientVersion:com.telemetrydeck.sdk"), true)
+    }
+
+    @Test
+    fun environmentMetadataProvider_allows_properties_to_be_set_in_advance() {
+        val appID = "32CB6574-6732-4238-879F-582FEBEB6536"
+        val config = TelemetryManagerConfiguration(appID)
+        val manager =  TelemetryManager.Builder().configuration(config).build(null)
+
+        manager.queue("type", "clientUser", mapOf("telemetryClientVersion" to "my value"))
+
+        val queuedSignal = manager.cache?.empty()?.first()
+
+        Assert.assertNotNull(queuedSignal)
+        Assert.assertEquals(queuedSignal?.payload?.contains("telemetryClientVersion:my value"), true)
+    }
+}