tests: improve testing (#80)

* chore: setup mini.test

* chore(ci): setup new test runner, install plugin deps

* chore(ci): test only on stable and nightly releases

* test: iferr

* test: struct_tags

* test: impl

* test: gotests

spec/fixtures/tests/method_output.go

@@ -0,0 +1,26 @@
+package fortest
+
+import "testing"
+
+func TestForTest_Add(t *testing.T) {
+	type args struct {
+		x int
+		y int
+	}
+	tests := []struct {
+		name string
+		tr   *ForTest
+		args args
+		want int
+	}{
+		// TODO: Add test cases.
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			tr := &ForTest{}
+			if got := tr.Add(tt.args.x, tt.args.y); got != tt.want {
+				t.Errorf("ForTest.Add() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}