Add test_dagascii.py + make find_pager() use DVC_PAGER

dvc/dagascii.py

@@ -31,13 +31,22 @@ def find_pager():
     if not sys.stdout.isatty():
         return pydoc.plainpager
 
-    if os.system("({}) 2>{}".format(DEFAULT_PAGER, os.devnull)) == 0:
-        pager_cmd = os.getenv(DVC_PAGER, DEFAULT_PAGER_FORMATTED)
+    env_pager = os.getenv(DVC_PAGER)
+    if env_pager:
 
-        def less_pager(text):
-            return pydoc.tempfilepager(pydoc.plain(text), pager_cmd)
+        def user_pager(text):
+            return pydoc.tempfilepager(pydoc.plain(text), env_pager)
 
-        return less_pager
+        return user_pager
+    else:
+        if os.system("({}) 2>{}".format(DEFAULT_PAGER, os.devnull)) == 0:
+
+            def less_pager(text):
+                return pydoc.tempfilepager(
+                    pydoc.plain(text), DEFAULT_PAGER_FORMATTED
+                )
+
+            return less_pager
 
     logger.warning(
         "Unable to find `less` in the PATH. Check out "

tests/unit/test_dagascii.py

@@ -0,0 +1,28 @@
+import mock
+import os
+
+from dvc import dagascii
+from dvc.env import DVC_PAGER
+
+
+def test_less_pager_returned_when_less_found():
+    with mock.patch.object(os, "system") as m:
+        m.return_value = 0
+        pager = dagascii.find_pager()
+
+    assert pager.__name__ == "less_pager"
+
+
+def test_plainpager_returned_when_less_missing():
+    with mock.patch.object(os, "system") as m:
+        m.return_value = 1  # any non-zero value
+        pager = dagascii.find_pager()
+
+    assert pager.__name__ == "plainpager"
+
+
+def test_tempfilepager_returned_when_var_defined():
+    os.environ[DVC_PAGER] = dagascii.DEFAULT_PAGER
+    pager = dagascii.find_pager()
+
+    assert pager.__name__ == "user_pager"