Add plot_spectrum method in TestW7 class.

- A call to this method is made by test_spectrum method
  which asserts spectrum quantities.

- The pass / fail status is mentioned on the plot itself,
  by passing a boolean parameter 'passed' to plot_spectrum.

- plot_spectrum is called in different ways from try and
  except blocks of test_spectrum, for the same.

tardis/tests/tests_slow/test_w7.py

@@ -104,46 +104,54 @@ def test_luminosity_inner(self):
                 self.obtained_radial1d_model.luminosity_inner)
 
     def test_spectrum(self):
-        assert_quantity_allclose(
+        try:
+            assert_quantity_allclose(
                 self.reference['luminosity_density_nu'],
                 self.obtained_radial1d_model.spectrum.luminosity_density_nu)
 
-        assert_quantity_allclose(
+            assert_quantity_allclose(
                 self.reference['delta_frequency'],
                 self.obtained_radial1d_model.spectrum.delta_frequency)
 
-        assert_quantity_allclose(
+            assert_quantity_allclose(
                 self.reference['wavelength'],
                 self.obtained_radial1d_model.spectrum.wavelength)
 
-        spectrum_fig = plt.figure()
-        spectrum_fig.suptitle("Deviation in spectrum quantities", fontweight="bold")
+            assert_quantity_allclose(
+                self.reference['luminosity_density_lambda'],
+                self.obtained_radial1d_model.spectrum.luminosity_density_lambda)
+
+            self.plot_spectrum(passed=True)
+        except Exception as e:
+            self.plot_spectrum(passed=False)
+            raise e
+
+    def plot_spectrum(self, passed):
+        plt.suptitle("Deviation in spectrum_quantities", fontweight="bold")
 
         # `ldl_` prefixed variables associated with `luminosity_density_lambda`.
-        ldl_axes = spectrum_fig.add_subplot(111)
-        ldl_axes.set_title("Deviation in luminosity_density_lambda")
-        ldl_axes.set_xlabel("N-th packet")
-        ldl_axes.set_ylabel("Relative error (1 - obtained / baseline)")
+        # Axes of subplot are extracted, if we wish to make multiple plots
+        # for different spectrum quantities all in one figure.
+        ldl_ax = plt.subplot(111)
+        ldl_ax.set_title("Deviation in luminosity_density_lambda")
+        ldl_ax.set_xlabel("N-th packet")
+        ldl_ax.set_ylabel("Relative error (1 - obtained / baseline)")
         deviation = 1 - (
             self.obtained_radial1d_model.spectrum.luminosity_density_lambda.value /
             self.reference['luminosity_density_lambda'].value)
 
-        try:
-            assert_quantity_allclose(
-                    self.reference['luminosity_density_lambda'],
-                    self.obtained_radial1d_model.spectrum.luminosity_density_lambda)
-
-            ldl_axes.text(0.9, 0.9, 'PASSED', transform=ldl_axes.transAxes,
+        if passed:
+            ldl_ax.text(0.8, 0.8, 'passed', transform=ldl_ax.transAxes,
                           bbox={'facecolor': 'green', 'alpha': 0.5, 'pad': 10})
-            ldl_axes.plot(deviation, "g+")
-        except Exception as e:
-            ldl_axes.set_yscale("log")
-            ldl_axes.text(0.9, 0.9, 'FAILED', transform=ldl_axes.transAxes,
+            ldl_ax.plot(deviation, "g+")
+        else:
+            ldl_ax.set_yscale("log")
+            ldl_ax.text(0.8, 0.8, 'failed', transform=ldl_ax.transAxes,
                           bbox={'facecolor': 'red', 'alpha': 0.5, 'pad': 10})
-            ldl_axes.plot(deviation, "rx")
-            raise e
+            ldl_ax.plot(deviation, "rx")
 
-        # Figure is saved in `tmp` directory of slow tests baseline data.
+        # Figure is saved in `tmp` directory right now, till a suitable way of
+        # saving them is decided.
         plt.savefig(os.path.join("/tmp", "spectrum_plot.png"))
 
     def test_montecarlo_properties(self):