add tests for the builder

t/builder.vim

@@ -0,0 +1,47 @@
+call airline#init#bootstrap()
+
+describe 'active builder'
+  before
+    let s:builder = airline#builder#new({'active': 1})
+  end
+
+  it 'should have a call to check mode'
+    let stl = s:builder.build()
+    Expect stl =~ '%{airline#check_mode()}'
+  end
+
+  it 'should transition colors from one to the next'
+    call s:builder.add_section('Normal', 'hello')
+    call s:builder.add_section('NonText', 'world')
+    let stl = s:builder.build()
+    Expect stl =~ '%#Normal#hello%#Normal_to_NonText#>%#NonText#world'
+  end
+
+  it 'should split left/right sections'
+    call s:builder.split()
+    let stl = s:builder.build()
+    Expect stl =~ '%='
+  end
+
+  it 'after split, sections use the right separator'
+    call s:builder.split()
+    call s:builder.add_section('Normal', 'hello')
+    call s:builder.add_section('NonText', 'world')
+    let stl = s:builder.build()
+    Expect stl =~ '%#Normal#hello%#Normal_to_NonText#<%#NonText#world'
+  end
+end
+
+describe 'inactive builder'
+  before
+    let s:builder = airline#builder#new({'active': 0})
+  end
+
+  it 'should transition colors from one to the next'
+    call s:builder.add_section('Normal', 'hello')
+    call s:builder.add_section('NonText', 'world')
+    let stl = s:builder.build()
+    Expect stl =~ '%#Normal_inactive#hello%#Normal_to_NonText_inactive#>%#NonText_inactive#world'
+  end
+end
+