Improve test coverage

In an effort to improve test coverage without being inefficient add a
new env variable `DO_FEATURE_MATRIX` to the test script. This is how we
do it over in `rust-secp256k1`, it enables good test coverage while not
having to run the whole matrix in every CI job.

Add cargo calls for each example because the current way we run the
examples does not work for those who configure the build output
directory to something other than the default.

Author: tcharding

contrib/test.sh

@@ -31,19 +31,29 @@ then
     exit 0
 fi
 
-# Test without any features first
-cargo test --verbose
+# Defaults / sanity checks
+cargo test
 
-# Test each feature
-for feature in ${FEATURES}
-do
-    cargo test --verbose --features="$feature"
-done
+if [ "$DO_FEATURE_MATRIX" = true ]
+then
+    # All features
+    cargo test --features="$FEATURES"
+
+    # Single features
+    for feature in ${FEATURES}
+    do
+        cargo test --features="$feature"
+    done
 
-# Also build and run each example to catch regressions
-cargo build --examples
-# run all examples
-run-parts ./target/debug/examples
+    # Run all the examples
+    cargo build --examples
+    cargo run --example htlc --features=compiler 
+    cargo run --example parse
+    cargo run --example sign_multisig
+    cargo run --example verify_tx > /dev/null
+    cargo run --example psbt
+    cargo run --example xpub_descriptors
+fi
 
 # Bench if told to (this only works with the nightly toolchain)
 if [ "$DO_BENCH" = true ]