Add a test for testing as a dependency

.travis.yml

@@ -1,4 +1,5 @@
 language: rust
+cache: cargo
 
 addons:
   apt:
@@ -17,11 +18,13 @@ addons:
 matrix:
   include:
     - rust: stable
-      env: DO_FUZZ=true DO_COV=true
+      env: DO_FUZZ=true DO_COV=true AS_DEPENDENCY=true
     - rust: beta
+      env: AS_DEPENDENCY=true
     - rust: nightly
-      env: DO_BENCH=true
+      env: DO_BENCH=true AS_DEPENDENCY=true
     - rust: 1.22.0
+      env: AS_DEPENDENCY=true
 
 script:
   - ./contrib/test.sh

contrib/test.sh

@@ -38,3 +38,12 @@ if [ "$DO_BENCH" = true ]
 then
     cargo bench --features unstable
 fi
+
+# Use as dependency if told to
+if [ -n "$AS_DEPENDENCY" ]
+then
+    cargo new dep_test
+    cd dep_test
+    echo 'bitcoin = { path = "..", features = ["use-serde"] }' >> Cargo.toml
+    cargo test --verbose
+fi