py: Use --test_env to permit easier usage of matplotlib in tests

bindings/pydrake/BUILD.bazel

@@ -456,6 +456,7 @@ drake_py_unittest(
 drake_py_binary(
     name = "math_example",
     srcs = ["math_example.py"],
+    add_test_rule = 1,
     isolate = 1,
     deps = [
         ":math_py",

bindings/pydrake/systems/BUILD.bazel

@@ -322,7 +322,6 @@ drake_py_binary(
     data = [
         "//examples/multibody/cart_pole:cart_pole.sdf",
     ],
-    test_rule_args = ["--test"],
     test_rule_timeout = "moderate",
     deps = [
         ":drawing_py",

bindings/pydrake/systems/drawing_graphviz_example.py

@@ -1,24 +1,14 @@
 import matplotlib.pyplot as plt
 
 from pydrake.common import FindResourceOrThrow
-from pydrake.geometry import (ConnectDrakeVisualizer, SceneGraph)
+from pydrake.geometry import ConnectDrakeVisualizer, SceneGraph
 from pydrake.lcm import DrakeLcm
 from pydrake.multibody.tree import UniformGravityFieldElement
-from pydrake.multibody.plant import MultibodyPlant
 from pydrake.multibody.parsing import Parser
+from pydrake.multibody.plant import MultibodyPlant
 from pydrake.systems.drawing import plot_system_graphviz
 from pydrake.systems.framework import DiagramBuilder
 
-import argparse
-
-parser = argparse.ArgumentParser()
-parser.add_argument("--test",
-                    action='store_true',
-                    help="Causes the script to run without blocking for "
-                         "user input.",
-                    default=False)
-args = parser.parse_args()
-
 file_name = FindResourceOrThrow(
     "drake/examples/multibody/cart_pole/cart_pole.sdf")
 builder = DiagramBuilder()
@@ -45,5 +35,4 @@
 
 plot_system_graphviz(diagram, max_depth=2)
 
-if not args.test:
-    plt.show()
+plt.show()

common/proto/test/call_python_test.py

@@ -27,7 +27,8 @@ def scoped_file(filepath, is_fifo=False):
 
 assert "TEST_TMPDIR" in os.environ, "Must run under `bazel test`"
 
-# Set backend so that the test does not open windows.
+# TODO(eric.cousineau): See if it's possible to make test usefully pass for
+# "Template" backend.
 os.environ["MPLBACKEND"] = "ps"
 
 SIGPIPE_STATUS = 141

examples/van_der_pol/BUILD.bazel

@@ -33,7 +33,6 @@ drake_py_binary(
     name = "plot_limit_cycle",
     srcs = ["plot_limit_cycle.py"],
     add_test_rule = 1,
-    test_rule_args = ["--test"],
     deps = [
         "//bindings/pydrake",
     ],

examples/van_der_pol/plot_limit_cycle.py

@@ -1,15 +1,7 @@
-import argparse
 import matplotlib.pyplot as plt
 
 from pydrake.examples.van_der_pol import VanDerPolOscillator
 
-parser = argparse.ArgumentParser()
-parser.add_argument("--test",
-                    action='store_true',
-                    help="Run without blocking for user input.",
-                    default=False)
-args = parser.parse_args()
-
 x = VanDerPolOscillator.CalcLimitCycle()
 
 fig, ax = plt.subplots()
@@ -19,5 +11,4 @@
 ax.set_xlabel('q')
 ax.set_ylabel('qdot')
 
-if not args.test:
-    plt.show()
+plt.show()

tools/bazel.rc

@@ -41,6 +41,9 @@ test --test_env=MOSEKLM_LICENSE_FILE
 # instance has a consistent, but non-default, LCM URL.
 test --test_env=LCM_DEFAULT_URL=memq://
 
+# Prevent matplotlib from showing windows (#11029).
+test --test_env=MPLBACKEND=Template
+
 ### A configuration that enables Gurobi. ###
 # -- To use this config, the GRB_LICENSE_FILE environment variable must be set
 # -- to the location of the Gurobi license key file. On Ubuntu, the GUROBI_PATH