Clean tests

In tests which inject template via stdin, inject the template via input
argument of subprocess.check_output rather than via command using echo
and pipe. Rationale: Less hassle with trailing LF, portability.

tests/test_cli.py

@@ -361,8 +361,8 @@ def test_broken_extensions_name_error(tmpdir):
 
 
 def test_render_template_from_stdin_to_stdout():
-    cmd = r'echo -n {{ foo }} | yasha --foo=bar -'
-    out = check_output(cmd, shell=True)
+    cmd = r'yasha --foo=bar -'
+    out = check_output(cmd, shell=True, input=b"{{ foo }}")
     assert out == b'bar'
 
 
@@ -379,24 +379,24 @@ def test_json_template(tmpdir):
 
 def test_mode_is_none():
     """gh-42, and gh-44"""
-    cmd = r'echo -n {{ foo }} | yasha -'
-    out = check_output(cmd, shell=True)
+    cmd = r'yasha -'
+    out = check_output(cmd, shell=True, input=b"{{ foo }}")
     assert out == b''
 
 
 def test_mode_is_pedantic():
     """gh-42, and gh-48"""
     with pytest.raises(subprocess.CalledProcessError) as err:
-        cmd = r'echo {{ foo }} | yasha --mode=pedantic -'
-        out = check_output(cmd, shell=True, stderr=subprocess.STDOUT)
+        cmd = r'yasha --mode=pedantic -'
+        out = check_output(cmd, shell=True, stderr=subprocess.STDOUT, input=b"{{ foo }}")
     out = err.value.output
-    assert out == b"Error: Variable 'foo' is undefined\n"
+    assert out.startswith(b"Error: Variable 'foo' is undefined")
 
 
 def test_mode_is_debug():
     """gh-44"""
-    cmd = r'echo -n {{ foo }} | yasha --mode=debug -'
-    out = check_output(cmd, shell=True)
+    cmd = r'yasha --mode=debug -'
+    out = check_output(cmd, shell=True, input=b"{{ foo }}")
     assert out == b'{{ foo }}'