cwd for running dashr tests - auto and override

CHANGELOG.md

@@ -4,6 +4,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 
 ## Unreleased
 ### Added
+- [#948](https://github.com/plotly/dash/pull/948) Support setting working directory for R apps run using the `dashr` fixture, primarily useful for tests with assets. `dashr.start_server` supports a `cwd` argument to set an explicit working directory, and has smarter defaults when it's omitted: if `app` is a path to an R script, uses the directory of that path; if `app` is a string, uses the directory the test file itself is in.
 - [#944](https://github.com/plotly/dash/pull/944)
   - Relevant `dash.testing` methods can now be called with either an element or a CSS selector: `select_dcc_dropdown`, `multiple_click`, `clear_input`, `zoom_in_graph_by_ratio`, `click_at_coord_fractions`.
   - Three new `dash.testing` methods: `clear_local_storage`, `clear_session_storage`, and `clear_storage` (to clear both together)

dash/testing/application_runners.py

@@ -7,6 +7,7 @@
 import threading
 import subprocess
 import logging
+import inspect
 
 import runpy
 import future.utils as utils
@@ -30,7 +31,7 @@ def import_app(app_file, application_name="app"):
 
     :Example:
 
-        >>> app = import_app('my_app.app')
+        >>> app = import_app("my_app.app")
 
     Will import the application in module `app` of the package `my_app`.
 
@@ -248,28 +249,52 @@ def __init__(self, keep_open=False, stop_timeout=3):
         self.proc = None
 
     # pylint: disable=arguments-differ
-    def start(self, app, start_timeout=2):
-        """Start the server with waitress-serve in process flavor."""
+    def start(self, app, start_timeout=2, cwd=None):
+        """Start the server with subprocess and Rscript."""
 
         # app is a R string chunk
-        if not (os.path.isfile(app) and os.path.exists(app)):
+        if (os.path.isfile(app) and os.path.exists(app)):
+            # app is already a file in a dir - use that as cwd
+            if not cwd:
+                cwd = os.path.dirname(app)
+                logger.info("RRunner inferred cwd from app path: %s", cwd)
+        else:
             path = (
                 "/tmp/app_{}.R".format(uuid.uuid4().hex)
                 if not self.is_windows
                 else os.path.join(
                     (os.getenv("TEMP"), "app_{}.R".format(uuid.uuid4().hex))
                 )
             )
-            logger.info("RRuner start => app is R code chunk")
-            logger.info("make a temporay R file for execution=> %s", path)
-            logger.debug("the content of dashR app")
+            logger.info("RRunner start => app is R code chunk")
+            logger.info("make a temporary R file for execution => %s", path)
+            logger.debug("content of the dashR app")
             logger.debug("%s", app)
 
             with open(path, "w") as fp:
                 fp.write(app)
 
             app = path
 
+            # try to find the path to the calling script to use as cwd
+            if not cwd:
+                for entry in inspect.stack():
+                    if "/dash/testing/" not in entry[1].replace("\\", "/"):
+                        cwd = os.path.dirname(os.path.realpath(entry[1]))
+                        break
+            if cwd:
+                logger.info(
+                    "RRunner inferred cwd from the Python call stack: %s",
+                    cwd
+                )
+            else:
+                logger.warning(
+                    "RRunner found no cwd in the Python call stack. "
+                    "You may wish to specify an explicit working directory "
+                    "using something like: "
+                    "dashr.run_server(app, cwd=os.path.dirname(__file__))"
+                )
+
         logger.info("Run dashR app with Rscript => %s", app)
         args = shlex.split(
             "Rscript {}".format(os.path.realpath(app)),
@@ -279,7 +304,7 @@ def start(self, app, start_timeout=2):
 
         try:
             self.proc = subprocess.Popen(
-                args, stdout=subprocess.PIPE, stderr=subprocess.PIPE
+                args, stdout=subprocess.PIPE, stderr=subprocess.PIPE, cwd=cwd
             )
             # wait until server is able to answer http request
             wait.until(lambda: self.accessible(self.url), timeout=start_timeout)

dash/testing/composite.py

@@ -21,10 +21,11 @@ def __init__(self, server, **kwargs):
         super(DashRComposite, self).__init__(**kwargs)
         self.server = server
 
-    def start_server(self, app):
+    def start_server(self, app, cwd=None):
 
-        # start server with dashR app, the dash arguments are hardcoded
-        self.server(app)
+        # start server with dashR app. The app sets its own run_server args
+        # on the R side, but we support overriding the automatic cwd
+        self.server(app, cwd=cwd)
 
         # set the default server_url, it implicitly call wait_for_page
         self.server_url = self.server.url