Add basic coverage reporting for RPC tests

Thanks to @MarcoFalke @dexX7 @laanwj for review.

qa/rpc-tests/test_framework/coverage.py

@@ -0,0 +1,101 @@
+"""
+This module contains utilities for doing coverage analysis on the RPC
+interface.
+
+It provides a way to track which RPC commands are exercised during
+testing.
+
+"""
+import os
+
+
+REFERENCE_FILENAME = 'rpc_interface.txt'
+
+
+class AuthServiceProxyWrapper(object):
+    """
+    An object that wraps AuthServiceProxy to record specific RPC calls.
+
+    """
+    def __init__(self, auth_service_proxy_instance, coverage_logfile=None):
+        """
+        Kwargs:
+            auth_service_proxy_instance (AuthServiceProxy): the instance
+                being wrapped.
+            coverage_logfile (str): if specified, write each service_name
+                out to a file when called.
+
+        """
+        self.auth_service_proxy_instance = auth_service_proxy_instance
+        self.coverage_logfile = coverage_logfile
+
+    def __getattr__(self, *args, **kwargs):
+        return_val = self.auth_service_proxy_instance.__getattr__(
+            *args, **kwargs)
+
+        return AuthServiceProxyWrapper(return_val, self.coverage_logfile)
+
+    def __call__(self, *args, **kwargs):
+        """
+        Delegates to AuthServiceProxy, then writes the particular RPC method
+        called to a file.
+
+        """
+        return_val = self.auth_service_proxy_instance.__call__(*args, **kwargs)
+        rpc_method = self.auth_service_proxy_instance._service_name
+
+        if self.coverage_logfile:
+            with open(self.coverage_logfile, 'a+') as f:
+                f.write("%s\n" % rpc_method)
+
+        return return_val
+
+    @property
+    def url(self):
+        return self.auth_service_proxy_instance.url
+
+
+def get_filename(dirname, n_node):
+    """
+    Get a filename unique to the test process ID and node.
+
+    This file will contain a list of RPC commands covered.
+    """
+    pid = str(os.getpid())
+    return os.path.join(
+        dirname, "coverage.pid%s.node%s.txt" % (pid, str(n_node)))
+
+
+def write_all_rpc_commands(dirname, node):
+    """
+    Write out a list of all RPC functions available in `bitcoin-cli` for
+    coverage comparison. This will only happen once per coverage
+    directory.
+
+    Args:
+        dirname (str): temporary test dir
+        node (AuthServiceProxy): client
+
+    Returns:
+        bool. if the RPC interface file was written.
+
+    """
+    filename = os.path.join(dirname, REFERENCE_FILENAME)
+
+    if os.path.isfile(filename):
+        return False
+
+    help_output = node.help().split('\n')
+    commands = set()
+
+    for line in help_output:
+        line = line.strip()
+
+        # Ignore blanks and headers
+        if line and not line.startswith('='):
+            commands.add("%s\n" % line.split()[0])
+
+    with open(filename, 'w') as f:
+        f.writelines(list(commands))
+
+    return True