1 files changed, 72 insertions, 0 deletions
diff --git a/spec/ruby/library/matrix/diagonal_spec.rb b/spec/ruby/library/matrix/diagonal_spec.rb
new file mode 100644
index 0000000000..ee84ac8c28
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+++ b/spec/ruby/library/matrix/diagonal_spec.rb
@@ -0,0 +1,72 @@
+require_relative '../../spec_helper'
+require_relative 'fixtures/classes'
+require 'matrix'
+
+describe "Matrix.diagonal" do
+  before :each do
+    @m = Matrix.diagonal(10, 11, 12, 13, 14)
+  end
+
+  it "returns an object of type Matrix" do
+    @m.should.is_a?(Matrix)
+  end
+
+  it "returns a square Matrix of the right size" do
+    @m.column_size.should == 5
+    @m.row_size.should == 5
+  end
+
+  it "sets the diagonal to the arguments" do
+    (0..4).each do |i|
+      @m[i, i].should == i + 10
+    end
+  end
+
+  it "fills all non-diagonal cells with 0" do
+    (0..4).each do |i|
+      (0..4).each do |j|
+        if i != j
+          @m[i, j].should == 0
+        end
+      end
+    end
+  end
+
+  describe "for a subclass of Matrix" do
+    it "returns an instance of that subclass" do
+      MatrixSub.diagonal(1).should.instance_of?(MatrixSub)
+    end
+  end
+end
+
+describe "Matrix.diagonal?" do
+  it "returns true for a diagonal Matrix" do
+    Matrix.diagonal([1, 2, 3]).diagonal?.should == true
+  end
+
+  it "returns true for a zero square Matrix" do
+    Matrix.zero(3).diagonal?.should == true
+  end
+
+  it "returns false for a non diagonal square Matrix" do
+    Matrix[[0, 1], [0, 0]].diagonal?.should == false
+    Matrix[[1, 2, 3], [1, 2, 3], [1, 2, 3]].diagonal?.should == false
+  end
+
+  it "returns true for an empty 0x0 matrix" do
+    Matrix.empty(0,0).diagonal?.should == true
+  end
+
+  it "raises an error for rectangular matrices" do
+    [
+      Matrix[[0], [0]],
+      Matrix[[0, 0]],
+      Matrix.empty(0, 2),
+      Matrix.empty(2, 0),
+    ].each do |rectangular_matrix|
+      -> {
+        rectangular_matrix.diagonal?
+      }.should.raise(Matrix::ErrDimensionMismatch)
+    end
+  end
+end