Add some minimal tests and fix a mistake

Author: naveen521kk

manim/mobject/svg/text_mobject.py

@@ -867,7 +867,7 @@ def text2svg(self):
             fontdesc = pangocffi.FontDescription()
             fontdesc.set_size(pangocffi.units_from_double(size))
             if family:
-                fontdesc.set_family("sans-serif")
+                fontdesc.set_family(family)
             fontdesc.set_style(style)
             fontdesc.set_weight(weight)
             layout.set_font_description(fontdesc)

tests/test_pango.py

@@ -0,0 +1,54 @@
+from manim import PangoText,START_X,START_Y,SVGMobject
+import os
+import cairocffi
+import pangocairocffi
+import pangocffi
+
+def test_general_text_svgobject():
+    """Checks number of submobjects generated when directly called using ``SVGMobject``"""
+	text = "hello"
+    size=1
+    folder = os.path.abspath(os.path.join("media","texts"))
+    if not os.path.exists(folder):
+        os.makedirs(folder)
+    filename = os.path.join(folder,'hello.svg')
+    a=PangoText(text,size=10)
+    pangoManim = os.path.join(folder,a.text2hash()+'.svg')
+    surface = cairocffi.SVGSurface(filename, 600, 400)
+    context = cairocffi.Context(surface)
+    context.move_to(START_X, START_Y)
+    layout = pangocairocffi.create_layout(context)
+    layout.set_width(pangocffi.units_from_double(600))
+    fontdesc = pangocffi.FontDescription()
+    fontdesc.set_size(pangocffi.units_from_double(size * 10))
+    layout.set_font_description(fontdesc)   
+    layout.set_text(text)
+    pangocairocffi.show_layout(context, layout)
+    surface.finish()
+    b = SVGMobject(filename)
+    assert len(a.submobjects) == len(b.submobjects)
+
+def test_render_text_svgobject():
+	"""Checks number of submobjects generated when directly called using ``SVGMobject``"""
+    text = "臂猿「黛比」帶著孩子"
+    size=1
+    folder = os.path.abspath(os.path.join("media","texts"))
+    if not os.path.exists(folder):
+        os.makedirs(folder)
+    filename = os.path.join(folder,'hello1.svg')
+    a=PangoText(text,size=10,font="amiri")
+    pangoManim = os.path.join(folder,a.text2hash()+'.svg')
+    surface = cairocffi.SVGSurface(filename, 600, 400)
+    context = cairocffi.Context(surface)
+    context.move_to(START_X, START_Y)
+    layout = pangocairocffi.create_layout(context)
+    layout.set_width(pangocffi.units_from_double(600))
+    fontdesc = pangocffi.FontDescription()
+    fontdesc.set_family("amiri")
+    fontdesc.set_size(pangocffi.units_from_double(size * 10))
+    layout.set_font_description(fontdesc)   
+    layout.set_text(text)
+    pangocairocffi.show_layout(context, layout)
+    surface.finish()
+    b = SVGMobject(filename)
+    assert len(a.submobjects) == len(b.submobjects)