Make test_contrasts.py ignore token.Whitespace (#1938)

With the VisibleWhitespaceFilter Pygments can be configured to replace
whitespace characters like spaces, tabs and newlines with Unicode
characters like ·, » and ¶ respectively.

The min_contrast metric is meant to represent the readability of a
style. Increasing it should mean that the style becomes more readable.

This commit therefore excludes the token.Whitespace contrast from the
min_contrast calculation, since giving whitespace characters a high
contrast would make them so intrusive that they would actually hinder
the readability of the source code.

tests/contrast/min_contrasts.json

@@ -1,39 +1,39 @@
 {
-  "default": 1.8,
-  "emacs": 1.8,
-  "friendly": 1.7,
-  "colorful": 1.9,
-  "autumn": 1.9,
+  "default": 2.6,
+  "emacs": 2.4,
+  "friendly": 2.2,
+  "colorful": 2.2,
+  "autumn": 2.2,
   "murphy": 1.4,
   "manni": 1.4,
   "material": 1.6,
   "monokai": 1.4,
-  "perldoc": 1.6,
-  "pastie": 1.9,
-  "borland": 1.9,
-  "trac": 1.9,
-  "native": 2.8,
+  "perldoc": 2.7,
+  "pastie": 2.5,
+  "borland": 2.3,
+  "trac": 2.3,
+  "native": 3.0,
   "fruity": 1.6,
   "bw": 21.0,
   "vim": 1.3,
   "vs": 3.6,
-  "tango": 1.0,
+  "tango": 2.4,
   "rrt": 1.0,
   "xcode": 5.1,
   "igor": 3.6,
   "paraiso-light": 1.3,
   "paraiso-dark": 1.3,
-  "lovelace": 3.1,
+  "lovelace": 3.5,
   "algol": 3.5,
   "algol_nu": 3.5,
   "arduino": 2.6,
-  "rainbow_dash": 1.6,
+  "rainbow_dash": 2.1,
   "abap": 2.5,
   "solarized-dark": 1.5,
   "solarized-light": 1.0,
-  "sas": 1.9,
-  "stata": 1.9,
-  "stata-light": 1.9,
+  "sas": 4.2,
+  "stata": 2.4,
+  "stata-light": 2.4,
   "stata-dark": 1.4,
   "inkpot": 1.0,
   "zenburn": 1.6,

tests/contrast/test_contrasts.py

@@ -14,6 +14,7 @@
 import sys
 
 import pygments.styles
+import pygments.token
 import wcag_contrast_ratio
 
 JSON_FILENAME = os.path.join(os.path.dirname(__file__), "min_contrasts.json")
@@ -42,6 +43,7 @@ def get_style_contrasts(style_cls):
             ttype,
         )
         for ttype, style in style_cls.list_styles()
+        if ttype != pygments.token.Whitespace
     ]