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external/boringssl/ssl/test/README.md

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+# BoringSSL SSL Tests
+
+This directory contains BoringSSL's protocol-level test suite.
+
+Testing a TLS implementation can be difficult. We need to produce invalid but
+sufficiently correct handshakes to get our implementation close to its edge
+cases. TLS's cryptographic steps mean we cannot use a transcript and effectively
+need a TLS implementation on the other end. But we do not wish to litter
+BoringSSL with options for bugs to test against.
+
+Instead, we use a fork of the Go `crypto/tls` package, heavily patched with
+configurable bugs. This code, along with a test suite and harness written in Go,
+lives in the `runner` directory. The harness runs BoringSSL via a C/C++ shim
+binary which lives in this directory. All communication with the shim binary
+occurs with command-line flags, sockets, and standard I/O.
+
+This strategy also ensures we always test against a second implementation. All
+features should be implemented twice, once in C for BoringSSL and once in Go for
+testing. If possible, the Go code should be suitable for potentially
+upstreaming. However, sometimes test code has different needs. For example, our
+test DTLS code enforces strict ordering on sequence numbers and has controlled
+packet drop simulation.
+
+To run the tests manually, run `go test` from the `runner` directory. It takes
+command-line flags found at the top of `runner/runner.go`. The `-help` option
+also works after using `go test -c` to make a `runner.test` binary first.
+
+If adding a new test, these files may be a good starting point:
+
+ * `runner/runner.go`: the test harness and all the individual tests.
+ * `runner/common.go`: contains the `Config` and `ProtocolBugs` struct which
+   control the Go TLS implementation's behavior.
+ * `test_config.h`, `test_config.cc`: the command-line flags which control the
+   shim's behavior.
+ * `bssl_shim.cc`: the shim binary itself.