Describe platform requirements for the compatibility tests.
diff --git a/java/compatibility_tests/README.md b/java/compatibility_tests/README.md
index 3a61e85..2465941 100644
--- a/java/compatibility_tests/README.md
+++ b/java/compatibility_tests/README.md
@@ -28,6 +28,10 @@
## How to Run The Tests
+We use a shell script to drive the test of different scenarios so the test
+will only run on unix-like environments. The script expects a few command
+line tools to be available on PATH: git, mvn, wget, grep, sed, java.
+
Before running the tests, make sure you have already built the protoc binary
following [the C++ installation instructions](../../src/README.md). The test
scripts will use the built binary located at ${protobuf}/src/protoc.
